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Vol.  1,  No.  7,  pp.  227-268,  Pis.  20-23  June  1,  1904 


THE   STRUCTURE   AND   REGENERATION 

OF  THE   POISON   GLANDS 

OF  PLETHODON 


B 

C.  O.  ESTERLY 


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Vol.  1,  No.  7,  pp.  227-268,  Pis.  20-24  June  1,  1904 


THE  STRUCTURE  AND  REGENERATION 
OF  THE  POISON  GLANDS 
OF  PLETHODON,/" 

BY          N^c 
C.  O.  ESTERLY.  i£. 


It  has  long  since  been  held  that  the  skin  glands  of  both  the 
Urodela  and  the  Auura  are  of  two  kinds.  This  distinction  was 
first  made  by  Ascherson  '40  in  an  investigation  of  the  glands  in 
the  web  of  live  frogs,  and  was  based  upon  the  size,  shape,  and 
location  of  the  glands  without  regard  to  function  or  microscopic 
structure.  That  the  skin  of  Amphibians  secretes  a  substance 
other  than  the  well-known  mucus,  and  clearly  poisonous,  has 
been  shown  by  many  physiological  and  toxicological  experiments 
and  investigations  (Albini  '56;  Boulenger  '92;  Calmels  '83; 
CappaiTelli  '83;  Dutarte  '89;  Gratiolet  and  Cloez  '51-'52; 
Hubbard  '03;  Phisalix-Picot  '00),  and  the  facts  gained  from 
experiment  are  upheld  as  far  as  possible  by  histological  evi- 
dence. Microscopic  examination  shows  that  there  is  more  than 
one  kind  of  gland.  (Ancel  '02;  Coghill  '99;  Eberth  '69; 
Eckhard  '49;  Engelmami  '72;  Hensche  '56;  Leydig  '76  a;  Pau- 
licki  '85;  Phisalix-Picot  '00;  Schultz  89;  Seeck  '91;  Stieda  '65; 
Szczesny  '67;  Wiedersheim  '86).  These  have  generally  been 
distinguished  as  granular  (Kornerdriisen)  and  clear,  according 
to  the  appearance  of  the  secretion  contained  in  them,  the  former 
having  been  almost  unanimously  looked  upon  as  making  the 
poison  series,  the  latter  the  mucous  series.  The  suggestion  has 
been  made,  however,  that  the  various  glands  are  only  the  young 
and  old  stages  of  one  sort  of  gland  (Junius  '98),  and  this  ques- 
tion will  receive  further  consideration  in  the  present  paper. 


R15 


'2'2S  University  of  California  Publication*.  [ZOOLOGV 

The  poison  glands  are  in  most  cases  much  larger  than  (hose 
of  the  mucous  variety,  and  their  enormous  cells  (Riesen/ellen  of 
Leydig)  completely  till  the  interior  of  the  gland  so  that  there  is 
no  lumen.  This  character  distinguishes  these  glands  from  the 
others,  which  are  provided  with  a  low,  cubical  epithelium  sur- 
rounding a  capacious  lumen.  (PI.  XX,  Fig.  2.)  The  mucous 
secretion  filling  the  lumen  is  very  distinct  from  the  heavily 
granular  contents  of  the  cells  of  the  poison  glands.  (PI.  XXIII, 
Fig.  31.)  The  two  sorts  of  glands  are  further  distinguished  by 
other  features,  chief  of  which  is  the  staining  reaction  of  the 
mucous  secretion  (Nicoglu  '93;  Hoyer  '90).  These  observers 
used  thionin  as  a  specific  stain  for  mucus  and  found  that  the 
small  glands  stain  rose-red  while  the  others  are  uncolored. 

The  foregoing  general  facts  have  been  determined  chiefly  upon 
the  Anura  and  the  various  European  Salamanders,  especially 
Triton  and  Salamaudra.  But  Pletliodon  oregonensis,  a  salaman- 
der found  about  Berkeley,  forms  a  particularly  interesting  object 
for  the  study  of  the  poison  glands  because  of  their  unusual 
development  on  the  tail  of  this  animal.  This  seems  to  be  a 
protective  character  associated  to  some  extent  with  the  ability  of 
the  animal  to  throw  off  its  tail  under  stress  of  circumstances.  It 
has  been  shown  by  experiment  that  the  secretion  of  the  glands 
of  the  tail  is  poisonous  or  obnoxious  to  certain  animals,  a  char- 
acter which  probably  belongs  to  the  dorsal  glands  (Hubbard,  '03) , 
which  are  very  large  and  much  more  developed  than  elsewhere  on 
the  body.  In  this  respect  Plethodon  appears  to  resemble  Triton 
cristatus.  (Capparelli  '83.)  However,  the  poison  glands  of 
Plethodon  are  not  confined  to  the  dorsum  of  the  tail;  much 
smaller  ones  are  found  011  its  ventral  surface  and  also  on 
the  trunk  and  head  of  the  animal,  intermingled  with  mucous 
glands,  which  occur  in  all  situations  where  the  poison  glands 
are  found. 

The  principal  question  considered  in  the  present  paper  con- 
cerns the  changes  occurring  in  the  formation  of  the  secretion 
and  its  expulsion  from  the  glands.  In  Plethodon  this  involves 
the  death  of  the  glands,  as  Seeck  ('92),  Nicoglu  ('93),  Vollmer 
( '93)  and  others  have  shown  for  other  Amphibia.  The  exhausted 
glands  are  here  renewed  or  replaced  in  the  manner  described  by 


VOL.  i.i  Esterly.— Poison  Glands  of  Plethodon.  ±29 

Heidenhain  ('98«).  Vollmer  ('!):!)  and  Nicoglu  ('93) .  This 
process  consists  in  the  growth  into  the  old  glands  of  a  new  and 
smaller  gland,  which,  however,  is  mucus  in  character,  contrary 
to  the  statements  of  Nicogln  ('93),  so  that  the  poison  glands 
develop  from  the  mucous  to  the  poison  variety.  This  has  been 
suggested  but  not  definitely  shown  by  Hover  ('90)  and  Junius 
('98),  and  distinctly  denied  by  all  other  investigators  of  the 
regeneration  of  these  glands.  Under  the  histological  structure 
of  the  glands  will  be  considered  some  new  points  in  the  muscu- 
lature, especially  as  to  the  presence  in  the  epidermis  of  an 
apparatus  for  closing  and  opening  the  duct.  The  innervation  of 
the  muscles  and  epithelium  of  the  glands  will  also  receive  atten- 
tion. 

This  work  was  done  under  the  direction  of  Professor  C.  A. 
Kofoid,  and  my  heartiest  thanks  are  due  him  for  very  kind 
assistance  in  every  way  and  for  criticism  of  results. 

MATERIAL   AND   METHODS. 

In  order  to  obtain  the  best  insight  into  the  structure  of  the 
glands  of  the  tail,  sections  in  three  planes  have  been  made  of 
that  entire  organ.  The  tissue  was  in  all  cases  perfectly  fresh 
and  was  fixed  in  Zenker's  fluid,  which  has  been  satisfactory  in 
all  respects.  Washing  in  70.%  iodine-alcohol  followed  the  use  of 
the  fixative. 

That  bony  tissue  might  not  hinder  the  passage  of  sections  in 
any  plane  through  the  whole  tail,  the  tissue  was  subsequently 
decalcified  in  a  5%  aqueous  solution  of  nitric  acid  for  from 
twelve  to  twenty-four  hours,  followed  by  immersion  in  a  5% 
aqueous  solution  of  sodium  sulphate  for  the  same  length  of  time, 
and  thorough  washing  in  running  water  for  from  twenty-four  to 
forty-eight  hours. 

Parafflue  sections  have  alone  been  used,  varying  in  thickness 
from  3^  to  10  microns.  The  sections  were  fixed  to  the  slide  by 
the  water- albumen  method,  and  in  all  cases  where  possible 
staining  was  done  on  the  slide. 

A  considerable  variety  of  stains  has  been  employed.  The 
most  successful  have  been  Mallory's  ('00)  connective  tissue  stain 
(acid  fuchsiu,  phospho-molybdic  acid,  anilin  blue-orange  G), 


230  University  of  California  Publications.  [ZOOLOGY 

Van  Gieson's  haemalum  and  piero-fuehsin,  and  the  iroii-haema- 
toxylins  of  Benda  and  Heidonhain.  I  have  found  it  of  consider- 
able advantage  to  increase  the  percentage  of  fuchsin  in  Malic >ry's 
stain  to  as  much  as  1.5  or  2%.  This  stain,  as  a  whole,  when 
successful  is  very  beautiful,  but  its  action  varies  most  unac- 
countably. The  staining  and  differentiation  will  be  perfect  in 
some  sections,  while  in  others  on  the  same  slide  the  differential 
coloration  will  fail  completely.  But  the  range  of  application  of 
the  stain  seems  to  be  almost  unlimited  except  for  purely  cytolog- 
ical  work. 

Other  stains  have  been  used,  such  as  Mayer's  neutral  and 
acid  haemalums  followed  by  eosin,  orange  G,  erythrosin  and 
Congo  red;  safranin  alone  or  in  combination  with  light  green; 
ferric  chloride  haematoxylin,  and  such  special  stains  as  the 
phosphotungstic  acid  haematoxyliu  of  Mallory  and  Cajal's  ('03) 
silver  nitrate-pyrogallic  acid  method  for  nerves,  Tanzer's  orcein 
for  elastic  fibres,  and  Mayer's  muei-carmine  as  a  mucus  stain. 

As  has  been  said, 'the  largest  poison  glands  of  Plethodon  are 
situated  on  the  back  of  the  tail,  and  in  cross  sections  (PI.  XX, 
Fig.  1,  p.gl.)  it  may  be  seen  that  they  lie  in  that  portion  of  the 
skin  covering  the  dorsal  half  of  the  tail.  Here  the  greatest 
development  is  in  the  glands  at  either  side  of  the  mid-dorsal 
line,  while  farther  down  on  the  sides  they  gradually  diminish 
until  they  are  considerably  smaller  and  not  readily  distinguished 
by  their  size  from  the  larger  mucous  glands.  (PL  XX,  Fig.  1, 
ni.f/l.)  The  coloration  also  of  the  tail  gives  a  clue  to  the  loca- 
tion of  the  largest  glands.  The  dorsal  half  of  the  tail  is  black 
or  brown,  while  the  ventral  half  is  orange  or  yellow,  and  the 
glands  under  consideration  are  confined  almost  entirely  to  the 
darker  portion.  The  mucus  glands  are  found  largely  on  the 
ventral  side  of  the  tail,  but  they  also  occur  along  the  dorsal  sur- 
face. In  this  region  they  lie  between  the  necks  of  the  large  glands. 

The  poison  glands  form  large  sacs,  extending  from  the  epi- 
dermis to  the  inner  layer  of  the  corium.  (PI.  XX,  Fig.  1.)  In 
shape  they  are  elongated,  with  oval  or  even  somewhat  rectangu- 
lar outline.  The  ducts  are  short,  and  the  transition  from  the 
body  of  the  gland  to  the  neck  and  duct  is  not  sharp  as  in  the 
mucous  glands,  which  are  regularly  flask-shaped. 


VOL.  i.]  Extrrhj. — Poison  Glands  of  Pie thodtm.  i>:!1 

It  ha.s  been  shown  (Hubliard  '().'!)  that  the  swollen  appear- 
ance of  the  tails  of  some  animals  is  due  to  the  increased 
development  of  the  poison  glands  posterior  to  the  well-marked 
constriction  found  just  behind  the  cloaca  in  such  cases.  That 
this  is  really  true  appears  in  the  study  of  a  series  of  sections  of 
a  swollen  tail  passing  from  the  tip  up  to  and  including  part  of 
the  eloacal  aperture.  In  the  constriction  the  dorsal  glands  are 
very  small  comparatively,  and  are  hei-e  no  larger  on  the  back  of 
the  tail  than  on  the  ventral  side.  But  behind  the  constriction 
their  development  is  much  greater,  and  one  may  trace  the  regular 
increase  in  size  as  the  series  passes  from  the  constriction  back  to 
the  enlarged  portion  of  the  tail.  Everywhere  in  the  tail,  except 
in  the  constriction  at  its  base,  the  difference  in  size  between  the 
glands  on  the  dorsal  and  ventral  surfaces  is  maintained. 

As  is  well  known,  the  bodies  of  all  the  glands  lie  in  a  spongy 
connective  tissue,  the  middle  layer  of  the  corium,  which  in  the 
region  of  greatest  development  of  the  poison  glands  is  increased 
enormously  in  thickness  (PL  XX,  Fig.  1,  m.c.l.),  being  alone 
from  one-sixth  to  one-fourth  or  more  of  the  dorsal- ventral  dimen- 
sion of  the  tail.  (Hubbard  '03. )  The  bottoms  of  the  large  glands 
rest  upon  or  come  very  close  to  the  inner  layer  of  the  corium. 
(PI.  XX,  Fig.  1,  i.e. I.) 

The  ducts  of  both  mucous  and  poison  glands  pass  through  the 
outer  corium  layer  and  the  epidermis,  the  long  axis  of  the  gland 
which  passes  through  the  duct  and  its  mouth  being  perpendicular 
to  the  surface  at  the  point  where  the  duct  opens  to  the  exterior. 

The  histological  structures  found  immediately  surrounding 
the  ducts  of  the  poison  glands  are  in  no  essential  points  different 
in  Plethodon  from  those  in  other  salamanders.  The  funnel  cells 
and  their  processes  (PI.  XX,  Figs.  1  and  2,  fl.c.)  are  present 
as  in  Triton  (Nicoglu  '93)  and  in  Salamandra  (Ancel  '02).  The 
membrane-like  structure  lining  the  duet  belongs  to  a  specialized 
cell  of  the  epidermis,  corresponding  to  the  "stoma  cell"  of  Eberth. 
As  Nicoglu  has  shown,  the  mouths  of  the  glands  lie  within  these 
cells,  processes  of  which  extend  down  in  the  ducts  about  as  far 
as  the  lower  limit  of  the  epidermis  or  a  little  farther.  (PL  XXIII, 
Fig.  27,  p.fl.c.)  The  prolongations  stain  black  in  iron  haema- 
toxylin,  reddish  in  Mallory's  and  yellow  in  Van  Gieson's  stain. 


232  University  of  California  Publications.  [ZOOM>QY 

In  addition  to  the  funnel  cells  proper,  Nicosia  lias  described  the 
arrangement  of  the  cells  in  the  epidermis  which  are  to  replace 
the  funnel  cells  as  they  are  thrown  off  at  the  time  of  moulting. 
The  same  condition  is  found  in  Plethodon  and  does  not  differ  at 
all  from  that  in  Triton  (Nicoglu  '03)  or  in  Salamandra  (Ancel 
'02).  (PL  XX,  Fig.  4;  PI.  XXIII,  Figs.  27,  28,  29,  30.  rn>.  ('.) 

As  further  evidence  that  the  cells  described  as  replacement 
cells  really  have  that  function,  Plethodon  shows  that  the  low  fi- 
ends of  the  replacement  cells,  especially  those  nearest  the  duct, 
extend  inward  as  do  the  prolongations  of  the  funnel  cells.  (PI. 
XXIII,  Fig.  27,  rep.  c.)  The  arrangement  of  the  former  very 
strongly  suggests  that  they  are  of  the  same  nature  and  function 
as  the  funnel  cells.  And  in  cross  sections  of  the  ducts  the 
replacement  cells  are  shown  rolled  one  within  the  other  as  in 
PI.  XX,  Fig.  4;  PI.  XXI,  Fig.  16,  rep.  C.  The  cell  first  to 
replace  the  one  thrown  off  at  moulting  immediately  surrounds 
the  duct;  the  cell  next  to  replace  this  one  lies  concentrically  out- 
side it,  and  so  on.  In  Mallorv's  stain  the  cell  boundaries  are 
very  distinct,  and  there  can  be  no  doubt  of  the  structure  as 
described  either  in  cross  or  in  longitudinal  section  of  the  ducts. 

The  walls  of  the  gland  sacs  proper  are  composed,  in  many 
Amphibia,  of  a  number  of  elements  which  have  been  described 
and  all  of  which  need  not  be  discussed  at  length  here.  In  the 
most  peripheral  layer  are  connective  tissue  and  elastic  fibrils,  as 
is  shown  by  the  use  of  Mallory's  connective  tissse  stain  for  the 
former  and  orcein  for  the  latter.  Nerves,  lying  in  this  layer,  also 
extend  over  the  gland.  Inside  the  connective  tissue  sheath,  MS 
it  is  generally  called,  lie  the  muscle  fibres,  and  next  to  them  the 
epithelium  of  the  gland. 

(See  in  this  connection  Drasch  '92,  '94;  Eberth  '69;  Eck- 
liard  '49;  Englemann  '72;  Hensche  '56;  Leydig  '76,  a,  b; 
Paulicki  '85;  Phisalix-Picot  '00;  Schuberg  '03;  Schultz  '89; 
Seeck '91;  Stieda '65;  Tonkoff '00;  Wiedersheim  '86.) 

Because  of  the  intimate  relation  between  the  connective 
tissues  of  the  gland  wall  and  those  of  the  corium,  it  is  necessary 
to  consider  in  more  detail  the  structures  of  the  inner,  middle 
and  outer  layers  of  the  corium.  Schuberg  ('03)  has  studied  the 
corium  of  Axolotl  most  minutely.  I  have  confirmed  his  results 


VOL.  i.i  Esterly.— Poison  Glands  of  Plethodvn.  233 

in  general  in  Plethodon,  and  particularly  as  to  the  relation  of 
the  connective  tissue  bundles  of  the  inner  layer  of  the  coriura  to 
those  of  the  middle  layer.  He  found  (p.  222)  that  columns  of 
connective  tissue  pass  perpendicularly  from  the  inner  into  the 
middle  layer,  and  seem  to  serve  as  mechanical  supports  for  the 
glands,  since  under  each  one  such  a  column  of  tissue  is  found. 
The  same  arrangement  occurs  in  Plethodon  except  that  the 
pi'i-pendicular  bundles  do  not  stand  beneath  the  glands,  but 
around  them,  as  can  be  seen  in  longitudinal  sections  of  the 
glands.  (PI.  XX,  Fig.  5,  c.t.b.)  In  spaces  between  the  large 
glands  or  on  the  ventral  side  of  the  tail,  the  bundles  from  the 
inner  layer  of  the  corium  can  be  seen  especially  well.  The  con- 
nective tissue  fibres  from  the  wall  of  the  gland  unite  with  the 
outer  layer  of  the  corium  which  then,  lying  next  the  muscle  layer 
of  the  gland,  passes  toward  the  surface  of  the  epidermis  and 
ends  on  the  side  of  the  neck  of  the  gland  about  a  third  of  the 
distance  between  the  inner  and  outer  boundaries  of  the  epider- 
mis. (PI.  XX,  Fig.  8;  PI.  XXIII,  Figs.  27,  31.)  This  appears 
in  both  longitudinal  and  cross  sections  of  the  ducts.  In  the 
latter  can  be  seen  a  crescent  of  connective  tissue  on  each  side  of  the 
duct  between  the  muscle  fibres  and  one  of  the  replacement  cells. 
(PL  XXIII,  Figs.  28,  29;  PI.  XXI,  Fig.  16,  c.t.)  Ancel  ('02,  PI. 
IX,  Fig.  22)  seems  to  have  shown  the  same  in  longitudinal  section. 
The  elastic  fibres  pass  through  the  inner  layer  of  the  corium 
into  the  middle  layer  in  company  with  the  connective  tissue 
bundles  as  Schuberg  ('03,  p.  231)  has  described.  The  elastic 
fibres  can  be  followed  around  the  glands,  and  over  them  in 
tangential  sections.  The  fibres  are  of  nearly  the  same  calibre 
throughout  and  all  of  them  take  the  same  general  direction, 
from  the  inner  corium  layer  perpendicularly  or  sharply  turned 
toward  the  outer  layer.  As  in  the  case  with  the  connective 
tissue  bundles  the  elastic  fibres  pass  at  once  around  or  over  the 
large  glands,  and  ar-e  not  found  arranged  perpendicularly  beneath 
them  as  in  Axolotl.  (Schuberg  '03,  p.  232,  Fig.  14.)  On  the 
sin-face  of  the  gland  they  are  branched  in  a  few  cases;  usually, 
however,  only  single  fibres  of  wavy,  curving  and  regular  outline 
are  visible,  ending  before  the  outer  corium  is  reached  (Schu- 
berg '03,  PI.  XXI,  Fig.  9,  t /./.). 


234  University  of  California  Publications.  [ZOOLOGY 

Between  the  connective  tissue  layer  and  the  gland  epithelium 
lies  the  layer  of  contractile  or  smooth  muscle  fibres.  These  were 
first  shown  histologically  by  Hensche  ('56),  though  before  him 
Ascherson  ('40)  had  observed  movements  of  the  living  glands. 
Since  this  time  there  has  been  no  doubt  of  the  existence  of 
muscles  in  the  walls  of  the  poison  glands  (Coghill  '99;  Drasi-h 
'89,  '92,  '94;  Eberth  '69;  Eckhard  '49;  Englemann  '72;  Heid- 
enhain  '93  a,  b;  Leydig  '76,  a,  b;  Massie  '94;  Nicoglu  '93; 
Paulicki  '85;  Phisalix-Picot  '00;  Schultz  '89;  Seeck  '91;  Stieda 
'65;  Szczesny  '67;  Vollmer  '93).  As  regards  the  smaller  series 
of  glands  the  question  seems  to  be  open.  The  absence  of  con- 
tractile fibres  on  them  has  been  used  as  a  character  to  separate 
them  from  the  large  glands.  The  muscles  of  the  large  glands 
are  arranged  in  a  single  layer  and  have  a  general  meridional 
direction  on  the  gland,  converging  toward  the  upper  pole.  The 
fibres  are  usually  simple  but  may  be  branched  (PL  XX,  Fig.  7) ; 
this  occurs  mostly  on  the  lower  part  of  the  gland.  Neither  do 
the  muscles  form  a  continuous  sheet  about  the  gland;  the  indi- 
vidual fibres  are  separated  by  spaces  of  greater  or  less  extent. 
I  have  not  been  able  to  find  with  certainty  muscles  on  glands 
which  are  mucous  in  nature. 

The  nuclei  of  the  contractile  cells,  contrary  to  the  description 
of  Nicoglu  ('93,  p.  437,)  and  such  figures  as  his  and  those  of 
Vollmer  ('93),  lie  in  the  upper  region  of  the  glands  just  outside 
the  uppermost  gland  cells,  yet  still  well  beneath  the  epidermis 
(PL  XX,  Fig.  6;  PL  XXIII,  Fig.  31,  »«,«.).  The  first  observer 
mentioned  has  shown  (his  PL  XXII,  Fig.  12)  the  nuclei  of  the 
muscle  cells  in  various  locations  about  the  periphery  of  the  glands; 
but  in  Plethodon  the  nuclei  have  a  constant  position  as  described 
and  are  found  only  there.  In  the  region  of  the  nuclei  the  muscle 
fibres  are  considerably  larger  than  elsewhere  on  the  gland,  as  is 
shown  in  PL  XX,  Fig.  8,  m.f.,  or  PL  XXIII,  Fig.  31,  m.f.,  so  that 
the  muscle,  especially  in  longitudinal  sections  of  the  glands,  seems 
to  bear  a  flask-shaped  expansion.  From  this  point  it  is  possible 
to  trace  a  single  fibre  very  nearhr  to  the  base  of  the  gland,  and 
also  outward  around  the  neck  of  the  gland  into  the  epidermis. 
(PL  XX,  Fig.  6.)  The  connection  of  the  muscles  with  the 
epidermis  has  been  reported  by  Nicogln  ('93)  and  Heidenhain 


vor,.  i.]  Kxti'i-li/.  —  Poison  Olands  of  PlethodoH.  -•!•"> 

('93  6),  and  the  arrangement  in  Plethodon  is  a  similar  one 
except  as  regards  the  presence  of  the  "Schaltstiick"  cells  described 
by  them.  In  Plethodon  the  "Schaltstiick"  is  not  demoiistrably 
present  except  in  one  or  two  questionable  cases  in  all  my  prepa- 
rations, and  Vollmer  ('93)  found  that  it  is  very  often  absent 
even  in  Triton.  There  can  be  no  doubt,  however,  that  the 
muscles  send  processes  into  the  epidermis.  This  is  especially 
well  shown  in  longitudinal  and  cross  sections  of  the  ducts. 

The  statement  that  the  muscle  nuclei  of  the  poison  glands  in 
Plethodon  lie  only  in  the  necks  of  the  glands,  instead  of  generally 
distributed  about  the  periphery  as  held  for  other  animals,  may 
be  supported  by  several  facts.  In  the  first  place,  longitudinal 
sections  of  the  glands  through  the  duct  and  mouth  show  two 
nuclei,  one  at  each  side  of  the  gland  where  the  sac  begins  to  pass 
over  into  the  duct.  In  sections  of  the  same  plane  which  pass  a 
little  to  one  side  of  the  duct  (PI.  XXI,  Fig.  10,  mf.,  nui.)  may 
be  seen  in  some  cases  the  obliquely  cut  ends  of  as  many  as  seven 
muscle  cells  each  with  its  nucleus  in  situ,  and  occupying  exactly 
the  position  relatively  of  the  two  lateral  nuclei  which  are  shown 
in  the  median  section.  There  can  be  no  doubt  of  their  structure. 

Cross  sections  of  glands  and  ducts  are  also  very  instructive 
on  this  point.  In  such,  especially  if  stained  in  Van  Gieson 
(PI.  XX,  Fig.  12) ,  there  are  shown  in  many  cases  the  light  yellow 
muscle  fibers  between  the  gland  cells  and  the  connective  tissue, 
when  the  plane  of  the  section  passes  more  deeply  through  the 
gland  than  the  position  of  the  nuclei  of  the  muscles.  But  when 
the  gland  is  cut  across  at  the  level  of  the  nuclei,  the  evidence 
gained  from  longitudinal  sections  is  even  more  strikingly  upheld. 
In  such  cross  sections  can  be  seen  as  many  as  twelve  or  fourteen 
muscle  fibres  stained  light  yellow  (in  Van  Gieson),  and  in  very 
sharp  contrast  to  them  the  brown  or  black  nuclei.  And  in  this 
region  the  section  of  the  muscle  is  larger  than  it  is  deeper  in  the 
gland;  this  corresponds  to  the  flask-shaped  enlargement  seen  in 
median  longitudinal  section  (PL  XX,  Fig.  8,  mf.).  If  a  series 
of  frontal  or  cross  sections  of  the  tail  is  studied,  it  will  be  found 
that  while  the  muscles  theinselves  can  be  traced  until  the  bottom 
of  the  gland  is  reached,  nuclei  never  appear  again  which  are 
unmistakably  those  of  the  muscle  fibres.  The  only  place  in 


236  University  of  California  Publicnfimis.  ! ZOOLOGY 

which  one  can  be  sure  that  he  is  dealing  with  nuclei  of  the  con- 
tractile fibres  is  in  the  location  above  described.  Hundreds  of 
sections  have  been  carefully  examined  and  there  has  never  been 
a  case  of  a  fully  formed  gland  in  which  the  muscle  nuclei  are 
situated  in  any  position  except  that  described.  Not  only  is  this 
true  in  stains  such  as  Mallory's  and  Van  Gieson's  but  also  in 
clear  nuclear  stains  like  iron  haematoxylin . 

That  those  observers  who  describe  muscle  nuclei  on  the 
periphery  of  the  gland  sacs  have  mistaken  connective  tissue 
nuclei  for  them,  seems  to  me  very  probable.  Nicoglu  ('93, 
p.  438)  says  that  the  nuclei  often  occupy  an  eccentric  position, 
so  that  even  with  oil  immersions  one  cannot  see  that  there  is 
any  protoplasm  of  the  muscle  cell  about  them.  His  description 
('93,  p.  436)  of  the  flattened  narrow  nuclei  of  the  muscle  cells 
applies  more  to  connective  tissue  nuclei.  That  these  occur  in 
the  walls  of  the  glands  has  been  observed  by  Paulicki  ('85, 
p.  158),  who  says:  "An  die  Driisen  treteu  gewohnlich 
sich  nach  oben  erstreckend  bindegewebige  Strange  init  Kernen." 
And  the  figures  of  Schuberg  ('03),  especially  Fig.  28,  show  that 
this  is  true  for  the  glands  of  Axolotl.  From  these  facts  and 
from  my  observations  on  Plethodon  it  is  clear  that  connective 
tissue  nuclei  closely  invest  the  glands,  and  evidence  is  added  to 
that  already  brought  forward  to  show  the  location  of  the  nuclei 
of  the  muscle  cells. 

The  processes  of  the  muscles  passing  into  the  epidermis  serve 
to  connect  the  fibres  with  the  outermost  layer  of  the  skin.  This 
has  been  shown,  as  said  before,  by  Heidenhain  ('93)  and  Nicoglu 
('93),  as  well  as  by  Ancel  ('02),  and  there  is  nothing  to  be 
added  to  the  description  given  by  the  former  except,  as  before 
stated  to  mention  the  frequent  non-occurrence  of  the  Schaltstuck 
as  such.  This  is  a  structure  described  as  containing  about  four 
cells  which  are  arranged  in  a  ring  about  the  neck  of  the  gland 
at  the. lower  boundary  of  the  epidermis.  The  cells  form  seem- 
ingly the  principal  points  of  insertion  of  the  muscle  fibres,  but 
this  cannot  be  so  in  Plethodon  where  the  Schaltstiick  is  virtually 
absent.  Otherwise  it  may  simply  be  said  that  the  upper  or  outer 
ends  of  the  muscle  fibres  pass  into  the  epidermis  and  end  between 
the  replacement  cells  of  the  funnel.  This  can  be  seen  fairly 


VOL.  i.]  Esterly. — Poison  Glands  of  Plethodon.  237 

well  in  cross  sections  of  the  gland  ducts  in  the  epidermis  where 
the  cut  ends  of  the  muscles  arc  seen  dose  beside  the  funnel  cell 
(PI.  XXIII,  Figs.  28,  20,  prol.  tii.f.).  In  good  longitudinal 
sections  of  the  ducts  the  muscles  (PI.  XXIII,  Fig.  27,  prol. 
m.f.)  are  seen  to  end  between  the  older  replacement  cells  which 
are  already  elongating  into  their  typical  form  (same,  rep.  r.). 
Xi. -no-lii  ('():!)  represents  the  endings  as  between  the  cells,  but 
Aucel  ('02)  seems  to  consider  them  as  special  parts  of  cells.  At 
any  rate  he  has  shown  (Fig.  22)  the  fibrils  as  within  cells  in  the 
epidermis.  I  have  not  been  able  to  find  such  structures  as  he 
shows;  there  can  be  hardly  any  doubt  that  the  prolongations  of 
the  gland  muscles  into  the  epidermis  end  between  the  replace- 
ment cells.  Nicoglu  and  Heidenhain  ('93)  and  Ancel  ('02)  have 
remarked  upon  the  existence  of  intercellular  bridges  between  the 
muscle  cell  on  the  one  hand  and  ectodermal  epithelial  cells  on  the 
other,  as  Nicoglu  says  (p.  440),  "von  ga7iz  ahulicher  Art  wie 
zwischen  den  Oberhautzellen  selbst." 

I  have  not  found  the  intercellular  bridges  in  Plethodon 
between  epithelial  and  muscle  cells,  but  all  the  facts  concerning 
the  connection  of  muscle  and  epidermal  cells  have  been  taken  as 
evidence  of  the  ectodermal  origin  of  the  muscles  of  skin  glands. 
This  has  been  so  often  commented  upon  that  it  is  useless  to  more 
than  call  attention  to  it  here.  The  evidence  gained  from  a  study 
of  the  development  of  the  glands  shows  that  the  muscle  fibres 
come  from  the  Malpighian  layer  of  the  epidermis  (Ancel  '02; 
Vollmer  '93;  Junius  '98).  This,  added  to  the  facts  already 
cited,  and  coupled  with  the  observations  of  many  investigators 
(Engelmann  '72;  Seeck'91;  Heidenhain '93;  Nicoglu '93)  seems 
fairly  conclusive  that  the  muscles  of  the  dermal  glands  are  of 
ectodermal  origin:  (Compare  also  in  case  of  sweat  glands, 
v.  Kolliker  '89;  Handbuch  des  Gewebelehre  des  Menschen,  pp. 
138  and  258). 

The  existence  of  a  sphincter  or  constrictor  muscle  for  the 
glands  has  been  claimed  by  Schultz  ('89),  who  described  a  band 
of  muscle  fibres  running  around  the  neck  of  the  gland  beneath 
the  meridional  layer.  This  observation  has  been  disproved  by 
Drasch  ('94)  and  Nicoglu  ('93),  and  I  have  been  unable  to  find 
such  a  structure  in  Plethodou.  And  there  is  no  evidence  of  the 


238  University  of  California  Publirntin-ns.  [ZOOLOGY 

epithelial  plug  of  Drasch  ('94)  for  restraining  the  contents  of 
the  gland  under  pressure.  Phisalix-Picot  ('00)  mentions  (pp. 
•44-45)  an  orbicular  muscle,  but  gives  no  description  or  drawing 
of  it,  so  that  her  meaning  is  obscure.  Dilator  muscles  for  tin- 
ducts  or  mouths  of  the  glands  have  never  been  described. 

However,  both  dilator  and  constrictor  muscles  occur  about 
the  mouths  of  the  poison  glands  of  Plethodon.  These  are  best 
shown  in  sections  of  the  epidermis  parallel  to  the  sin-face,  stained 
in  Mallory's  connective  tissue  stain,  which  are,  of  course,  also 
cross  sections  of  the  ducts.  All  three  sets  of  gland  muscles  may 
very  often  be  seen  in  one  such  section  (PI.  XXIII,  Fig.  30,  con. 
m.,  dil.  m.,  m.f.;  Figs.  28,  29  also).  In  these  cases  it  will  be  seen 
that  the  duct  (l.<l.)  in  the  epidermis  is  oval  in  cross  section,  and 
that  at  each  end  of  the  oval  is  a  triangular  mass  of  fibres,  stain- 
ing red  in  Mallory,  as  do  the  muscles  on  the  body  of  the  gland. 
The  fibres  converge  toward  the  duct  and  insert  upon  the  replace- 
ment cells  nearest  the  funnel  in  such  a  way  that  by  contracting 
they  will  bring  the  lips  of  the  duct  together  and  so  close  or 
greatly  diminish  its  lumen  (PI.  X^Q,  Fig.  16).  The  con- 
strictor fibres  are  differentiations  of  the  cell  whose  large  nucleus 
(PI.  XXI,  Figs.  14,  16;  PI.  XXII,  Fig.  28,  iute.tf.iiM.), 
stands  at  the  ends  of  the  elliptical  opening  of  the  duct.  The 
fibres  lie  within  this  cell  as  can  be  especially  well  seen  in  longi- 
tudinal sections  of  the  glands  which  do  not  pass  through  the 
duct.  Here  it  appears  that  the  cell  of  which  the  constrictor 
fibres  are  a  part,  together  with  its  nucleus,  lies  in  the  deepest 
layer  of  the  epidermis  immediately  upon  the  outer  layer  of  the 
corium.  This  cell  seen  in  surface  view  is  equal  in  extent  to 
several  of  the  neighboring  epidermal  cells,  but  in  cross  section 
it  is  very  much  flattened  (PI.  XXI,  Fig.  13).  Ancel  ('02) 
has  figured  such  a  cell,  but  gives  no  clue  as  to  its  function. 

The  dilator  fibres  belong  to  the  same  cell  of  which  the  con- 
strictors form  a  part,  and  are  at  a  slightly  lower  level  seemingly 
than  the  latter.  The  action  of  the  dilator  is  two  fold.  Some 
fibres  pass  around  the  ends  of  the  oval  opening  of  the  duct 
(PI.  XXIII,  Fig.  28,  dil.  m.;  PI.  XXI,  Fig.  14)  and  when  they 
shorten  they  tend  to  separate  the  lips  of  the  lumen  more  widely, 
by  pressing  at  the  ends  of  the  ellipse.  This  is  evident  when  it 


VOL.  i.]  Esterly. — Poixnn  (Unmix  t>f  I'lrfhtiilon.  239 

is  seen  that  the  mass  of  dilators  is  often  concave  in  outline 
toward  the  center  of  the  duct  (PL  XXIII,  Fig.  28:  I'l.  XXI,  Fig. 
!.">,  ilil.m.),  so  that  in  contraction  the  fibres  first  mentioned 
pull  in  the  general  direction  of  the  major  axis  and  toward  the 
center  of  the  ellipse.  Other  dilator  fibres  attach  at  the  edges  of 
the  duct  near  the  end  (PI.  XXI,  Fig.  14),  and  in  shortening  pull 
in  the  direction  of  the  minor  axis  of  the  ellipse,  thus  widening 
the  lumen  by  spreading  its  walls  at  the  tips  of  the  oval.  (PI.  XXI, 
Fig.  14. )  The  entire  effect  of  the  dilator  fibres  is  to  make  the 
aperture  of  the  duct  nearly  circular,  thus  offering  freer  exit  to 
the  secretion.  Their  action  would  be  to  open  the  duct  from  the 
form  shown  in  PI.  XXI,  Fig.  16,  to  that,  for  example,  in  PI. 
XXIII,  Fig.  30. 

The  fact  that  the  constrictor  and  dilator  fibres  lie  entirely 
within  the  epidermis  need  not  militate  against  their  having  the 
function  of  muscles,  for  in  the  case  of  the  intrinsic  gland  muscu- 
lature it  has  been  well  established  that  it  has  an  ectodermal 
origin.  It  is  certain  that  the  arrangement  and  appearance  of 
the  fibres  described  as  constrictor  and  dilator  muscles  are  such  as 
to  suggest  very  strongly  both  that  nature  and  function.  The 
coloration  in  Mallory  is  exactly  that  of  the  smooth  muscles  of 
the  glands ;  and  the  convergence  of  the  constrictor  fibres  to  their 
insertion  in  a  position  where  contraction  would  close  the  duct; 
the  endings  of  the  dilators  in  places  to  be  of  greatest  advantage 
in  widening  it  when  the  muscles  contract — all  these  facts  lead 
one  to  conclude  that  he  has  to  deal  with  an  apparatus  for  closing 
and  opening  the  ducts  of  the  glands. 

The  muscles  of  the  poison  glands,  as  has  been  said,  immedi- 
ately envelop  the  secretory  cells.  The  entire  gland  is  filled  with 
enormous  cells,  the  generally  recognized  "Giftzellen"  of  many 
authors  or  the  "giant  cells"  of  Leydig.  In  such  glands  a  lumen 
does  not  exist;  this  is  especially  well  shown  in  sections  of  the 
tail  of  a  tadpole  38  mm.  in  length,  in  which  the  cell  boundaries 
are  distinct,  the  secretion  not  yet  being  present  in  sufficient 
quantities  to  obliterate  them.  There  it  will  be  seen  that  the  ends 
of  the  cells  are  in  contact  with  the  middle  of  the  gland,  thus 
doing  away  with  any  trace  of  a  lumen  (Nicoglu  '93;  Seeck  '91; 
Calmels  '83).  A  glance  at  the  figures  will  serve  to  distinguish 


240  University  of  California  Publication*.  IZOOI.OM 

in  this  respect  the  poison  and  mucous  glands;  the  latter  have 
capacious  lumens  (PL  XX,  Fig.  2),  often  filled  with  a  clear 
secretion.  The  large  gland  cells  each  have  a  number  of  nuclei 
(Nicoglu  '93;  Drasch  '92),  not  over  four  in  Plethodon.  They 
are  round  or  oval,  of  regular  outline,  and  lie  normally  upon  or 
very  near  the  wall  of  the  gland,  and  so  at  the  base  of  the  cells. 
The  internal  structure  of  the  nuclei  is  simple.  There  is  a  scanty 
network  and  few  chromatin  granules;  usually  also  one  or  two 
nucleoli. 

The  cells  and  nuclei  of  the  small  or  mucous  glands  are  distinct 
in  every  way  from  those  of  the  poison  glands.  The  cells  are  low 
and  cubical  and  show  a  filar  structure  (psendo-filar,  Nicoglu  '93) . 
This  is  seen  in  sections  stained  either  with  Van  Gieson,  Mallory 
or  iron  haematoxyliu .  The  nuclei  are  smaller  than  those  of  the 
poison  glands,  and  angular  instead  of  regular  in  outline.  They 
invariably  stain  intensely  black  in  iron  haematoxylin,  remaining 
so  when  the  nuclei  of  the  giant  cells  have  decolorized  to  a  very- 
faint  gray  (PI.  XX,  Figs.  2,  3;  PI.  XXII,  Figs.  18,  19,  20). 

A  general  comparison  of  the  two  sorts  of  glands  might  be 
instituted  in  some  such  terms  as  these.  The  poison  glands  are 
very  much  larger  than  the  mucous  glands,  and  have  contractile 
walls;  the  mucous  glands  lack  this  character.  The  extreme 
dimensions' of  the  former  on  the  tail  are  approximately  from  1400 
microns  in  length  and  380  microns  in  breadth  to  680  microns  in 
length  by  200  microns  in  breadth,  and  half  the  latter  figures  on 
the  body.  The  mucus  glands  vary  from  93  by  90  microns  on  the 
tail  to  60  by  40  microns  on  the  body.  This  alone,  without 
closer  inspection,  would  serve  to  generally  distinguish  the  two 
varieties  of  glands;  but  in  addition  the  poison  glands  have  no 
lumina,  the  cells  and  nuclei  are  much  larger  than  in  the  other 
glands  (mucous  average  about  11  microns  in  greatest  diameter, 
poison  about  20  microns)  and  stain  differently;  and  above  all 
the  character  of  the  secretion  is  vastly  different. 

As  might  be  gathered  from  the  name  often  applied  to  them, 
the  secretion  in  the  poison  glands  is  composed  of  granules. 
These  are  of  varying  size,  and  the  cells  are  entirely  filled  with 
them.  The  mass  stains  from  red  (PI.  XXIII,  Fig.  31,  sec.)  or 
reddish  yellow  to  a  dark  purple  in  Mallory;  in  Van  Gieson  the 


VOL.  i.]  Kstfrhj. —  Poison  Glands  of  Plethodon.  241 

color  is  as  a  whole  yellow  with  a  tinge  of  red.  In  iron  haema- 
toxylin  some  granules  stain  (I'l.  XXII,  Fig.  1<S)  black:  but  at 
times  one  can  detect  in  sonic  granules  a  clear  outer  portion 
which  takes  the  counter  stain  (erythrosin,  etc.),  while  the  central 
part  stains  dark  black,  and  others  which  take  only  the  counter 
stain. 

The  mucous  secretion,  on  the  other  hand,  reacts  very  differ- 
ently, as  does  the  cytoplasm  of  the  mucous  cells,  which  can  be 
easily  distinguished  from  their  secretion.  Here  the  reactions  are 
typically  those  of  mucus.  Mallory's  stain,  which  colors  mucus  in 
the  sublingual  of  a  cat  a  clear  blue  in  two  minutes,  stains  in  the 
same  wiiy  both  the  cells  and  the  secretion  of  the  small  glands. 
This  same  stain  beautifully  differentiates  the  mucus  in  the  goblet 
cells  of  the  oesophagus  and  intestine  of  Plethodon.  I  have  not 
been  able  to  obtain  the  reaction  in  these  gland  cells  with  thionin , 
in  which  Nicoglu  places  so  much  confidence  as  a  mucous  stain. 
Hubbard  ('03)  has  had  the  same  difficulty.  However,  inucicar- 
mine,  a  specific  mucous  stain,  gives  the  mucous  reaction  after 
twelve  or  twenty-four  hours  in  both  the  glands  of  Plethodon  and 
the  sublingual  of  the  cat.  The  use  of  Van  Gieson's  stain  clearly 
differentiates  the  small  gland  from  the  large  ones.  In  the  former 
the  cells  and  the  secretion  are  stained  a  clear  red  or  pink, 
without  a  trace  of  yellow  as  in  the  poison  glands.  Orcein  also, 
which  has  been  described  as  a  mucous  stain,  colors  the  cytoplasm 
of  the  mucous  gland  cells  a  deep  brown,  and  has  absolutely  no- 
effect  on  the  granular  secretion  of  the  poison  glands.  The  iron 
haematoxylin  is  of  little  use  in  revealing  the  mucous  nature  of  the 
small  glands,  since  they  take  only  the  counter  stain  except  for 
the  nuclei.  These  become  a  deep  black  as  already  said.  But 
this  method  at  least  serves  to  distinguish  the  two  sorts  of  glands 
aside  from  the  nuclear  staining,  in  that  the  secretion  of  the  small 
glands  never  takes  the  haematoxylin,  as  do  the  granules  of  the 
large  glands. 

From  these  distinctions  as  to  the  primary  character  of  the 
two  classes  of  glands,  we  are  led  to  consider  the  histogenesis  of 
the  secretion.  It  has  been  generally  held  that  this  process  is  not 
the  same  in  the  mucous  and  poison  glands.  Seeck  ('91),  p.  55, 
holds  that  the  secretory  cells  are  of  two  sorts,  "solche  die  als. 


242  University  of  California  Publications. 

Zt'lli'ii  erhalten  bleiben  und  Driisensecret  secern  tren  (Schleim- 
driisen),  und  andere,  cleren  Protoplasma  sich  in  fVinkorniges 
Driisenseeret  metamorphosirt  wobei  die  Zellen  vollkommen  auf- 
gebracht  werden,  zu  Gruude  gehen,  so  dasz  man  ilm>  in  Zerfall 
begriffenen  Kernen  in  Driisensecret  findcn  kann  (Korner-oder 
Giftdriisen)."  Nicoglu  ('93),  p.  447,  finds  that  the  cells  of  the 
poison  glands  "wenn  ihre  Stuude  gekommen  ist,  wandelu  sie  sich 
in  toto  in  Secretniasse  um."  But  up  to  this  time  they  act  as 
other  gland  cells  in  elaborating  and  retaining  a  secretion  in  their 
interior,  as  the  pancreas  cells  do  zymogen  granules.  Sclmltz 
('89)  does  not  think  that  all  the  cells  of  a  gland  are  destroyed  at 
the  same  time,  but  such  as  do  form  a  part  of  the  secretion  mass 
must  be  regenerated;  indicating  that  they  are  destroyed  in  the 
process  of  secretion.  Drasch  ('94)  merely  states  that  the  poison 
glands  of  the  salamander,  if  completely  emptied,  pass  entirely 
away,  and  are  replaced  by  new  glands.  Observations  of  the 
glands  at  various  times  after  emptying  show  regressive  changes 
in  all  the  layers.  Vollmer  ('93)  also  has  described  the  process 
of  solution  of  the  Leydig  cells  after  strong  electrical  stimulation 
of  the  glands,  and  has  made  careful  statements  regarding  the 
appearance  of  the  emptied  glands.  The  conditions  in  Plethodon 
almost  duplicate  those  he  has  described. 

It  seems  pretty  well  founded,  then,  that  the  poison  gland 
cells  pass  bodily  into  the  secretion  mass.  But  a  distinction 
should  be  made  here,  as  Nicoglu  has  done,  between  the  secretion 
mass  as  that  thrown  out,  and  the  secretion  material,  which  is 
the  formed  substance  in  the  cells.  There  is  no  evidence  of  the 
disintegration  and  solution  of  cells  in  the  full  but  not  discharged 
gland.  It  is  only  when  for  some  reason  the  glands  are  emptied 
that  the  degenerative  processes  are  discerned.  Otherwise  the 
formed  secretion  is  retained  within  the  cells,  which  remain  in  a 
normal  condition  at  such  times. 

This  review  of  the  literature  describes  very  well  the  processes 
which  go  on  in  Plethodon;  PI.  XXI,  Fig.  17,  will  show  the 
appearance  of  a  gland  on  the  day  it  was  emptied.  It  has 
shrunken  greatly  in  size;  as  compared  with  others  of  the  same 
animal  which,  for  some  reason  were  not  emptied,  from  three 
hundred  microns  in  diameter,  say  to  one  hundred  microns.  The 


VOL.!.]  Vxtfi-li/.  —  PoixoH  Glands  of  Plethodon.   .  243 

nuclei  which  in  full  glands  lie  at  the  bases  of  the  cells,  are  in  tliis 
case  in  the  inner  parts  of  the  cells,  and  are  larger  and  clearer 
and  in  a  state  of  disintegration.  In  some  places  only  outlines 
or  shadows  of  nuclei  can  lie  seen.  Often  they  became  shrunken 
and  irregular  in  outline  when  the  gland  is  emptied.  The  entire 
appearance  of  emptied  glands  would  lead  to  the  conclusion  that 
their  time  of  functional  activity  is  at  an  end. 

The  mucous  glands,  on  the  other  hand,  never  reveal  such 
changes.  It  seems  correct  to  say  that  the  processes  there  are 
like  those  in  milk  glands,  where  parts  of  the  cell  bodies  ai-e 
thrown  oft'  as  secretion,  while  the  remaining  portions  in  time 
repeat  the  same  processes  of  secretion.  Nussbaum  ('82,  p.  302; 
speaks  of  the  heads  or  inner  portions  of  the  mucous  gland  cells 
of  Salamander  as  discharged  on  stimulation. 

If  it  is  true  then,  as  it  seems  to  be,  that  the  poison  glands  are 
changed  bodily  into  the  mass  of  secretion,  we  must  look  to  some 
source  for  their  replacement,  if  the  animal  is  to  have  their  con- 
tinued protection.  Nussbaum's  conclusions  should  be  cited  here 
('S2,  p.  336)  as  bearing  on  the  general  topic  of  death  of  gland 
cells  through  secretory  activity,  and  their  renewal.  He  says 
secretion  consists  in  the  formation  and  elaboration  of  the  mother- 
substance  of  the  secretion  material,  the  changing  of  this  in  the 
cells  and  in  emptying  the  secretion  when  ready,  out  of  the  cells. 
''Wie  alles  Lebende  aus  uns  unbekannten  Ursachen  abstirbt 
und  neuen  Generationen  Platz  macht,  so  gehen  auch  nach  einer 
gewissen  Zeit  Driisenzellen  zu  Grunde  und  werden  von  leben- 
skriiftigen  Nachbarzellen  ersetzt.  Sterben  aller  Zellen  gleich- 
zeitig  ab,  so  1st  die  Driise  vernichtet  wie  eine  Protozoen  Colouie. 
Die  Secretion  mag  wohl  die  Zelle  abniitzen;  die  Zelle 
wird  altern.  Der  Ort  der  Secretion  ist  aber  nicht  gleich  bedeu- 
tend  mit  Zellentod;  er  ist  eine  energische  Lebensthatigang." 

In  this  particular  case  of  the  skin  glands  of  Amphibia,  a 
definite  process  of  replacement  goes  on,  occurring  in  Plethodon 
in  the  way  described  for  other  salamanders  by  Nicoglu  ('93), 
Heidenhain  ('93)  and  Vollmer  ('93),  and  not  as  Junius  ('98) 
claims,  by  entirely  new  origin.  The  former  observers  find  that 
inside  the  old  poison  glands  there  lies  a  second  smaller  gland, 
possessing  a  lumen.  This  small  sac  is  to  replace  the  older  gland 


244  University  of  California  PnblirutioHs.  [ZOOLOGY 

and  lies  always  between  the  musculature  and  epithelium  of  the 
latter.  Nicoglu  ('93)  iinds  that  the  new  glands  possess  "all  the 
epithelial  parts  of  the  old  gland  with  the  exception  of  the 
"Schaltstiick."  Whether  this  statement  is  to  include  also  the 
muscle  fibres,  he  does  not  say;  his  figures  show  muscle  cells 
lying  upon  the  ingrowing  gland,  but  there  is  no  reference  to 
prove  that  they  belong  to  it  rather  than  to  the  old  gland. 
However,  Vollmer  ('93)  says  that  the  new  gland  contains  both 
gland  cells  and  smooth  muscle  fibres,  which  arise  as  does  the 
gland  bud,  from  the  Malpighian  layer  of  the  epidermis. 

The  place  of  origin  of  the  replacement  glands  is  found  by 
Nicoglu  ('93)  and  Heidenhain  ('93r/)  in  the  very  small,  flattened 
cells  immediately  adjoining  the  Schaltstiick  and  lying  inside  the 
gland.  Vollmer  ('93)  on  the  other  hand  concludes  that  the 
place  of  origin  of  the  new  gland  "ist  das  Keimlager  des  Rete 
Malpighi.  Auch  die  von  Heidenhain  erwahnten  unscheinbarer 
Zellenelemente,  denen  er  die  Bildung  der  Driisenknospe  zusch- 
reibt  stammen  vom  Rete  Malpighi."  There  is  no  reason,  he 
says,  why  the  new  glands  inside  the  old  ones  should  not  differ- 
entiate as  do  the  first  glands  in  the  course  of  their  development. 

In  Plethodon  the  method  of  renewal  of  the  worn-out  glands 
is  as  these  authors  have  described,  but  there  is  no  evidence 
showing  the  source  of  the  replacement  glands,  and  the  subject 
must  be  dismissed  with  the  above  references  to  the  literature. 

But  whatever  the  source  of  the  new  glands,  there  can  be  no 
doubt  that  in  every  old  gland  without  exception  there  is  a  small 
sac  or  replacement  gland.  This  is  always  found  in  those  glands 
which  have  not  been  discharged  (PI.  XXIII,  Pig.  31),  as  well  as 
in  those  which  have  been  and  show  the  most  extensive  degen- 
erative phenomena.  In  this  respect  Plethodon  seems  to  differ 
from  Triton  (Vollmer  '93).  This  author  states  that  the  growth 
of  the  new  gland  is  initiated  when  the  old  glands  are  emptied. 
Nicoglu  ('93)  mentions  the  fact  that  the  old  poison  glands  con- 
tain the  smaller  sacs,  but  does  not  say  definitely  whether  or  not 
the  destructive  processes  must  have  set  in  before  the  the  new 
gland  makes  its  appearance.  But  in  Plethedon  the  presence  of 
the  replacement  gland  is  not  dependent  on  the  secretory  processes 
in  the  large  glands.  The  former  are  present  in  the  glands  of  an 


VOL.  i.]  E.itcHij. — Poison  Glands  of  Plethodon.  '24'} 

animal  thirty-eight  mm.  long  which  are  not  filled  with  secretion. 

We  have  to  deal  then,  in  these  cases,  with  the  regeneration 
of  a  gland  by  a  gland.  Individual  cells  are  not  broken  down, 
and  then  renewed  by  the  growth  of  new  cells  as  Schultz  ('8!)) 
maintains,  and  as  seems  to  be  implied  by  Calmels  ('83),  who 
finds  that  the  young  gland  cells  are  indifferent  elements  which 
may  develop  into  either  poison  or  mucous  cells,  so  that  a  gland 
may  be  poisonous  only  in  part. 

The  question,  however,  as  to  whether  a  poison  gland  is 
replaced  only  by  a  poison  gland  is  still  to  be  considered.  May 
not  these  be  renewed  by  glands  which  to  begin  with  are  mucous 
in  character?  That  is,  may  not  a  specific  poison  secreting 
epithelium  be  replaced  through  mucous  cells,  and  gland  by  gland 
instead  of  cell  by  cell  ?  These  inquiries  have  been  raised  by 
Xicoglu,  and  he  says  ('93,  p.  425)  that  a  mucous  cell  never  goes 
over  into  a  poison  cell,  or  vice  versa,  and  Schultz  ('89)  also  says 
that  mucous  glands  are  always  only  mucous  glands,  and  poison 
glands  only  poison  glands  (p.  33),  and  therefrom  we  are  to  sup- 
pose that  the  same  is  true  of  the  individual  cells,  as  he  finds  that 
cells  replace  cells. 

Still  the  evidence  gained  by  a  study  of  the  poison  glands  of 
Plethodon  indicates  rather  strongly  that  we  have  to  deal  with 
<i  production  of  poison  glands  from  mucous  glands  fiilirely. 
Nicoglu  has  already  shown  that  in  Triton  a  mucous  gland 
may  sometimes  replace  a  poison  gland  entirely,  but  he 
very  strongly  opposes  the  idea  that  the  function  of  such  a  gland 
ever  changes.  He  holds  (p.  435)  that  the  condition  of  mucus 
within  poison  gland  is  a  functional  adaptation,  because  the 
animal  needs  more  mucous  glands  than  are  on  hand.  Everything 
goes  to  show  that  in  Plethodou,  on  the  other  hand,  the  occasional 
method  of  regeneration  described  by  Nicoglu  is  the  only  one. 
The  replacement  glands  already  described  stain  blue  without 
exception  in  Mallory,  which  has  been  shown  to  be  a  mucous  stain. 
The  contrast  between  the  blue  of  the  mucus  and  the  red  of  the 
granular  secretion  is  very  sharp  (PI.  XXIII,  Fig.  31).  The 
mucous  reactions  described  for  Van  Gieson,  orcein  and  mucicar- 
inine,  are  shown  invariably  in  the  replacement  glands  as  in  the 
mucous  glands  outside,  and  the  correspondence  of  the  replacement 


'J-H>  University  of  Cnl-ifm-niii   I'tiliHriilions.  [ZOOLOGY 

glands  stained  in  iron  haematoxylin  with  the  other  mucous  glands 
is  just  as  complete  (compare  I'l.  XX,  Figs.  2  and  3). 

There  can  be  nothing  clearer  than  the  reaction  of  the  new- 
glands  to  ATallory's  stain.  The  blue  color  is  present  in  every  case 
as  shown  by  a  study  of  hundreds  of  glands.  In  the  very  large 
glands  on  the  back  of  the  tail  the  ingrowing  glands  never  reach  be- 
yond a  certain  size,  such  as  is  shown  in  PI.  XXIIT,  Fig.  31.  This 
may  possibly  be  due  to  some  effect  of  the  poison  which  would 
hinder  the  growth  of  the  small  gland,  or,  as  seems  more  likely, 
the  new  gland  does  not  develop  because  it  is  hemmed  in  and 
hindered  in  its  growth  by  the  pressure  of  the  large  amount  of 
secretion  in  the  old  gland.  Drasch  ('94)  has  made  this  sugges- 
tion previously,  bnt  does  not  say  where  the  replacement  glands 
are  located.  But  in  all  the  small  poison  glands  which  lie  along 
the  sides  of  the  tail  and  also  on  the  dorsal  and  ventral  surfaces, 
particularly  in  the  constriction,  can  be  seen  all  stages  of  devel- 
opment of  the  mucous  glands  within  them,  from  the  small  buds  to 
new  glands  which  have  almost  entirely  replaced  the  old  ones. 
The  small  poison  glands  differ  from  the  largest  ones  in  no  other 
respect  than  in  size,  and  for  that  reason  it  seems  fair  to  conclude 
that  the  processes  of  regeneration  going  on  in  them  are  charac- 
teristic, and  typical  of  those  believed  to  occur  under  certain 
circumstances  in  the  large  glands  of  Plethodon,  and  as  observed 
in  other  salamanders.  There  are  many  cases  to  be  seen  in 
Plethodon  in  which  some  glands  are  so  far  replaced  by  a  new 
mucous  gland  that  only  a  faint  crescent  of  granular  secretion  can 
be  seen,  the  rest  of  the  contents  being  mucus.  In  other  cases" 
the  amount  of  granular  material  is  a  little  greater,  and  in  still 
others  we  may  see  the  gland  half  granular  and  half  mucus 
(PI.  XX,  Fig.  3;  PI,  XXII,  Figs.  18,  19,  20).  In  all  these  the 
granular  portions  stain  as  do  the  same  parts  of  the  large  glands, 
while  the  remainder  reacts  to  Mallory  and  the  other  stains  as  do 
the  small  sacs  in  the  large  glands  and  the  mucous  glands  outside 
of  these. 

To  sum  up  the  foregoing  we  may  say  that  the  small  glands 
within  the  large  ones  react  like  known  mucous  glands  to  Mallory 's 
stain  and  mucicarmine,  and  in  the  same  way  so  far  as  the  nuclei 
of  the  replacement  and  mucous  glands  of  the  tail  are  concerned, 


VOL.  i.]  Eslrrly.  —  PO'IXOH  Blonds  of  Plethodon,  247 


to  iron  haematoxylin.  That  is,  both  the  mucous  cells  and  those 
of  the  replacement  glands  stain  blue  in  Mallory.  red  or  pink  in 
Van  Gieson,  and  both  have  a  fibrillar  structure.  The  mucous 
reaction  is  also  given  with  inucicarinine.  And  finally,  the  nuclei 
of  the  ingrowing  gland  fundaments  always  stain  intensely  black 
in  iron  haematoxylin,  as  do  the  nuclei  of  the  mucous  glands. 

The  facts  just  related  have  been  gained  entirely  from  a  stud\ 
of  preparations  made  from  material  taken  from  unstimulated 
animals,  that  is  those  not  irritated  prior  to  immersion  in  killing 
fluids.  The  evidence  along  this  line  is  stronger  and  more  con- 
vincing in  the  case  of  an  animal  which,  without  stimulation  of  any 
kind  other  than  such  as  might  have  occurred  in  nature,  got  rid 
of  a  great  deal  of  the  secretion  in  the  glands  of  the  tail  and  then 
cast  that  organ  off,  as  if  it  could  be  of  110  further  use.  The 
animal  in  question,  when  first  observed,  was  seen  to  be  entangled 
head  down  between  some  pieces  of  bark  in  the  terrarium  in 
which  it  was  confined.  This  seemed  to  irritate  the  salamander 
very  much,  for  when  it  freed  itself  it  began  moving  quickly 
about,  swinging  its  tail  from  side  to  side  like  an  angry  cat.  The 
tail,  during  this  time,  became  covered  with  a  very  abundant 
white  secretion,  After  about  five  minutes  of  such  behavior  on 
the  part  of  the  animal,  when  I  merely  touched  the  tail  it  was 
suddenly  thrown  off,  the  break  being  in  the  constriction  back  of 
the  cloaca. 

The  tail  was  put  into  Zenker's  fluid  after  about  fifteen  min- 
utes, and  sections  made  later.  Here  the  likeness  between  the 
fundaments  in  the  empty  poison  glands  and  the  mucous  glands 
could  not  be  more  complete.  In  all  the  stains  used  the  appear- 
ances are  exactly  the  same.  The  cells  of  the  mucous  glands  are 
much  higher  than  in  other  animals  seen,  stain  a  lighter  blue  in 
Mallory,  and  have  a  vesicular  structure  approaching  granular, 
rather  than  the  filar  structure  usually  seen.  Even  so,  the 
replacements  glands  cells  are  their  exact  counterparts,  and  show 
the  same  reactions  to  Van  Gieson,  mucicarmine,  and  iron  haema- 
toxylin, as  well  as  Mallory  's  stain. 

It  seems  hardly  possible  that  the  cells  of  the  mucous  glands 
could  have  so  changed  their  structure  and  appearance  in  fifteen 
or  twenty  minutes,  though  the  increase  in  height  and  consequent 


248  University  of  California  Publications.  [ZOOLOGY 

diminution  in  size  of  the  lumen  of  the  gland,  together  with  the 
vesicular  structure  of  the  cells,  would  lead  one  to  think  that  they 
are  in  the  way  of  becoming  granule  or  poison  cells.  But  what- 
ever the  interpretation  put  upon  this  appearance,  and  to  what- 
ever source  it  is  due,  it  must  be  admitted  that  the  fundaments  in 
the  old  poison  glands  have  undergone  the  same  processes  and 
their  histological  characters  are  now  exactly  similar  to  those  of 
the  mucous  glands. 

Further  evidence  that  the  glands  are  originally  all  of  the 
same  character  may  be  gained  from  the  literature.  Ancel  ('02), 
who  has  followed  very  closely  the  development  of  the  skin  glands 
in  salamander,  considers  that  the  large  glands  represent  organs 
more  completely  differentiated  than  the  small  glands  toward  a 
special  functional  adaptation,  though  both  in  early  development 
are  absolutely  alike  (pp.  269,  283.)  Jiuiius  ('98)  believes 
that  there  is  but  one  kind  of  gland  in  the  skin  of  the  frog  and 
probably  of  all  Amphibia,  and  that  the  various  glands  of  the 
authors  are  young  and  old  forms  or  developing  stages  of  them. 
He  says  further  that  in  the  frog  he  has  not  seen  the  regeneration 
described  by  Vollmer  and  Nicoglu,  and  declares  that  atrophied 
glands  are  replaced  by  wholly  new  ones  developed  by  down- 
growths  of  epiderm  cells  into  the  cutis.  According  to  him, 
small  glands  represent  young  stages  of  large  ones,  and  the  for- 
mer are  equivalent  to  the  non-contractile  or  mucous  glands,  while 
the  latter  are  the  dark,  contractile,  granule  or  poison  glands. 

Again,  Hoyer  ('90,  p.  354)  finds  that  in  some  poison  glands 
of  the  salamander  single  cells  or  groups  of  cells  lying  between 
the  non-staining  large  granular  cells  take  on  a  red-violet  color 
in  thionin  (which  he  employs  as  a  specific  mucous  stain).  He 
makes  the  suggestion  merely:  "Moglicher  Weise  deutet  dieses 
eigenthiimliche  Verhalten  auf  eine  genetische  Beziehung  der  in 
den  Driisenzellen  enthaltenen  mueinahnlichen  Substanz  zu  dem 
giftige  Secrete."  And  finally,  the  observation  of  Phisalix-Picot 
('00)  that  the  secretion  of  the  mucous  glands  of  the  Salamander 
is  poison,  seems  to  me  to  bear  along  this  line  of  a  correlation 
between  the  so-called  mucous  glands  and  the  poison  glands. 

Evidence  in  this  direction  also,  further  than  that  already 
advanced  seems  to  be  indicated  in  the  poison  glands  of  Plethodon. 


VOL.  i.]  Etttfrly. — Poison  Glands  of  Plethodon,  24!) 

Here  there  is  very  frequently  a  distinct  blue  tinge  to  the  <jni»nl<n- 
secretion.  This  may  possibly  be  because  the  metamorphosis 
from  ''a  mucus-like  substance  to  the  poison  secretion"  is  not 
entirely  completed.  At  any  rate  one  is  impressed  with  the  like- 
lihood that  there  is  mucous  material  in  the  poison  glands  outside 
of  that  contained  in  the  replacement  glands. 

In  the  discussion  of  the  replacement  of  the  poison  glands  by 
those  of  the  mucus  variety,  it  has  been  shown  that  every  large 
gland  has  within  it  the  fundament  of  a  new  gland  which  to  all 
stains  for  mucus  except  thionin  gives  the  mucous  reaction,  and 
which  is  also  the  exact  counterpart  of  the  small  glands  having 
the  mucous  secretion.  The  fact  that  only  in  poison  glands  of 
smaller  size  are  found  evidences  that  they  are  entirely  replaced 
by  mucous  glands,  maybe  explained  on  the  ground  that  there  the 
amount  of  granular  secretion  is  not  sufficient  to  mechanically 
hinder  the  growth  of  the  new  replacement  gland.  The  actual 
transition  stages  from  mucous  to  granular  secretion  have  not  been 
observed  in  my  material. 

If  we  make  the  assumption  in  view  of  these  facts  that  the 
glands  of  mucous  character  in  the  poison  glands  develop  only  into 
mucous  glands  on  the  death  of  the  latter,  we  are  forced  to  one  of 
two  conclusions:  either  that  the  small  glands  outside  the  large 
ones,  especially  in  Plethodon  on  the  dorsal  surface  of  the  tail, 
become  the  poison  glands,  or,  on  the  other  hand,  that  when  the 
latter  are  once  destroyed  there  is  no  return  to  such  struct- 
ure except  by  developing  anew  according  to  the  embryonic 
type. 

The  latter  process  is  going  on  continually  in  large  as  well  as 
in  small  animals,  as  can  be  readily  seen  by  inspection  of  sections. 
Hut  it  seems  that  the  fundaments  are  all  alike  to  begin  with 
(Ancel  '02) ;  as  this  author  says,  the  solid  gland  buds  in  which 
a  cavity  is  formed  do  not  undergo  further  important  morpho- 
logical transformations,  and  constitute  the  mucous  glands.  Those 
which  remain  solid,  however,  continue  their  development  in  other 
ways  and  form  the  poison  glands  (p.  269) .  It  seems  to  me  that 
this  is  equivalent  to  saying  that  in  embryological  development 
the  poison  glands  pass  through  a  mucous  stage  to  reach  their  final 
form  and  character.  It  certainly  lends  evidence  to  the  view 


250  University  of  California  l*ubrH-<iii<>ns.  [ZOOLOGY 

expressed,  that  the  glands  which  are  to   replace  the  worn-out 
poison  glands  are  originally  mucus  in  character. 

There  is  no  reason  to  believe,  however,  that  the  replacement 
glands  are  functionless  during  the  life  of  the  poison  glands  in 
which  they  lie.  Even  the  smallest  replacement  glands  have 
distinct  ducts  and  epithelium,  and  in  some  cases  it  is  absolutely 
certain  that  they  have  elaborated  a  secretion  similar  in  every 
respect  to  that  of  the  mucous  glands. 

It  is  very  probable  that  under  all  ordinary  conditions  the  small 
glands  in  the  large  ones  secrete  mucus,  and  in  thi>  sense  art- 
adaptations;  not  because  the  animal  through  some  unusual 
external  conditions  has  come  to  need  more  mucous  ghinds  as 
Nicoglu  ('93)  says,  but  rather  because  under  normal  environ- 
ment there  is  always  need  of  more  mucus  than  can  be  secreted 
by  the  glands  outside  the  poison  glands,  especially  when  the 
latter  are  so  closely  crowded  together  as  on  the  back  of  the  tail 
in  Plethodon.  And  much  evidence  goes  to  show  that  under 
stress  of  necessity  such  mucus  secreting  glands  become  by 
replacement  the  more  highly  specialized  poison  glands  and  take 
on  a  particular  function,  that  of  forming  a  substance  protecting 
the  animal  from  its  enemies  (Hubbard  '03.) 

The  nerve  supply  of  the  skin  of  Amphibia  has  been  a  favorite 
subject  of  study  for  many  years.  Most  investigators  have  limited 
themselves  to  the  terminations  in  the  sense  organs  of  the  skin 
and  in  or  on  the  ordinary  epidermal  cells  (Pfltzner  '82;  Cauini 
'83;  Preukel  '86;  Massie  '94;  Herrick  and  Coghill  '98;  Coghill 
'99) .  The  innervation  of  the  glands  has  received  less  attention. 

Eckhard  ('49)  first  showed  that  the  glands  could  be  emptied 
by  stimulating  the  anterior  roots  of  the  cerebro-spinal  nerves, 
but  did  not  consider  the  structure  of  the  nerve  endings.  Eberth 
('69)  found  that  there  is  a  network  of  very  fine  fibres  close  upon 
the  glands;  Englemann  ('72)  came  to  the  same  conclusion  and 
showed  farther  that  from  the  nerves  about  the  gland  fine  twigs 
are  given  off  to  the  contractile  cells.  Openschowski  ('82) 
describes  a  network  of  nerves  surrounding  the  glands,  as  well 
as  an  iutracellular  net;  but  from  his  figures  it  is  hard  to  believe 
that  the  structures  he  shows  are  nerves.  Drasch  ('89)  also  experi- 
mentally proved  the  efficacy  of  nerve  stimulation  iu  obtaining 


VOL.  i.]  l-lxferly.  —  Poimm  Qlands  of  Plfthodon.  '1~>\ 


from  the  glands,  as  docs  I'hisalix-I'icot  ('00).  Ebertli 
and  Hunge  ('92)  liave  described  free  nei-ve  fibres  which  seem  to 
end  with  knobs  outside  the  epithelium  of  the  ball  of  the  thumb 
of  the  male  frog-  Loeb  ('9(5)  has  also  shown  how  closely  the 
glands  of  Amblystoma  are  connected  with  the  central  nervous 
system.  In  189S  Herrick  and  Coghill  were  able  to  show  the 
existence  an  intimate  connection  of  nerve  fibres  with  the  walls 
of  the  glands,  but  were  unable  to  discover  the  exact  relation 
of  the  fibres  to  the  gland  cells.  They  also  described  the 
plexus  of  nerves  beneath  the  corium  as  being  composed  of  two 
sorts  of  fibres;  larger  ones  connected  with  the  nerve  bundles 
of  the  central  system,  and  smaller  ones  which  in  part,  at  least, 
originate  in  ganglion  cells  in  the  corium.  Sehuberg  ('03)  has 
criticised  the  results  of  these  authors,  contending  that  many  or  all 
of  the  nerve  bundles  described  are  really  connective  tissue 
bundles,  and  that  the  ganglion  cells  are  the  "Mastzellen"  he 
himself  figures. 

^lassie  ('!)!))  continuing  the  work  of  Herrick  and  Coghill, 
(•(insiders  the  same  arrangement  of  fibres  beneath  the  corium, 
and  also  shows  that  nerves  end  on  the  muscles  of  the  "ental" 
glands.  He  finds  that  nerve  fibres  passing  from  the  nerve  bundle 
plexus  under  the  corium  are  intimately  connected  with  the  ental 
glands,  and  seem  distinct  from  the  nerves  supplying  the  muscles. 
"It  seems,  therefore,  that  there  are  two  groups  of  nerves  passing 
to  the  glands  of  the  ental  series;  the  one  attaching  by  the  typical 
endings  to  the  enveloping  muscle  cells,  the  other  ramifying 
promiscuously  over  the  surface  of  the  gland."  (p.  59.) 

In  the  study  of  the  nerves  of  the  poison  glands  of  Plethodon, 
three  methods  have  been  relied  upon;  namely,  the  silver  nitrate- 
pyrogallic  acid  method  of  Cajal,  and  Mallory's  phosphotungstic 
acid  haematoxylin  and  fuchsin-orauge  G-anilin  blue  methods. 
The  last  named  gave  most  excellent  results,  while  of  the  other 
two  Cajal's  was  only  indifferently  successful. 

The  haematoxylin  of  Mallory  stains  only  the  sheaths  of  the 
nerves  and  so  it  is  of  no  value  in  tracing  the  axis  cylinders,  since, 
as  is  well  known,  the  nerves  lose  the  medullary  sheaths  on  pass- 
ing into  the  corium.  Beneath  the  corium,  however,  the  nerves 
can  readily  be  followed  by  this  method.  In  some  instances  fibres 


2.V2  ['Hirerxity  of  California  Publications.  [ZOOI/IOY 

are  shown  rniuiing  for  long  distances  beneath  the  corium,  and 
branches  can  even  be  seen  to  turn  toward  the  epidermis,  but  all 
traces  of  them  arc  lost  as  soon  as  they  enter  the  corium. 

The  other  method  of  Mallory  gives  like  results  as  far  as  the 
distribution  of  the  nerves  beneath  the  corium  is  concerned.  In 
cross  sections  of  the  tail  it  is  often  possible  to  trace  a  fibre  from 
the  roots  leaving  the  cord  out  to  the  corium.  Sometimes  this 
may  be  seen  in  one  section;  in  many  cases  two  or  three  neigh- 
boring serial  sections  will  show  the  same.  The  plexus  beneath 
the  corium  is  shown  best,  as  a  whole,  in  frontal  sections  of  the 
tail.  Here  itwill  be  seen  that  the  nerves  are  very  HIIIHO'OHX,  and 
with  the  method  in  hand  can  be  traced  to  their  connections  with 
the  cord.  There  can  be  no  question  as  to  the  presence  of  the 
nerve-bundle  layer  of  the  plexus  that  Herrick  and  his  pupils  have 
shown;  but  as  regards  the  stratum  of  glauglion  cells,  it  seems 
to  me  that  Schuberg's  criticism  holds  good.  At  any  rate  neither 
of  Mallory' s  methods  reveals  such  a  structure,  and  this  would  at 
least  seem  strange  in  view  of  the  beautiful  staining  of  other  nerv- 
ous elements.  In  cross  sections  of  the  tail,  Mallory's  fuchsin 
method  shows  nerves  running  in  or  immediately  beneath  the 
inner  corium  layer.  At  times  several  fibres  are  in  view  at  once, 
being,  however,  of  different  sizes. 

Within  the  corium  the  distribution  of  the  nerves  to  the  glands 
is  not  apparent  in  sections  which  pass  through  the  gland,  owing 
to  the  exceedingly  small  size  of  the  fibres.  But  when  the  peri- 
phery of  the  gland  is  just  denuded,  the  nervous  elements  are 
shown  very  clearly.  In  such  cases  it  will  be  seen  that  there  is  a 
feltwork  of  many  verg  fine  fibres  closely  investing  the  gland,  end- 
ing upon  the  muscle  fibres  and  around  the  nuclei  of  the  gland  cells. 

The  endings  upon  the  muscles  are  shown  both  by  Cajal's 
method  and  Mallory's  fuchsin  stain,  and  in  some  cases  are  typi- 
cal (PI.  XXII,  Figs.  25  and  26)  as  described  by  Huber  and 
Dewitt  ('97)  and  Coghill  ('99) .  That  is,  they  are  equipped  with 
terminal  expansions  or  bulbs  which  lie  on  the  muscles.  In  many 
cases  fine  branching  fibres  can  be  clearly  seen  lying  upon  the 
muscle  layer.  These  pass  over  ultimately  into  the  finest  of 
slender  twigs  which  without  terminal  expansions  always  lie  on  a 
muscle  fibre  and  end  there  (PI.  XXII,  Fig.  26.) 


VOL.  i.]  Estrrly.  —  Poison  C/'/nds  of  PHJimJon.  253 

The  fibres  in  the  perinnclcar  endings  are  of  much  the  same 
character  as  those  of  the  muscles.  There  are  many  instances 
which  are  very  clear  of  basket  structure  about  the  nuclei  of  the 
large  glands  (PI.  XXII,  Figs.  21,  22.  PI.  XXIII,  Fig.  30). 
[  have  not  been  able  to  discover  connections  between  the  fibres  and 
the  nuclei,  though  in  at  least  one  ease  (PL  XXII,  Figs.  23,  24) 
I  lie  fibres  end  in  knobs  which  lie  directly  on  the  nucleus.  The 
latter  seems  usually  to  be  surrounded  only  by  a  basket  of  fine 
fibres.  Bethe  ('94)  has  described  three  sorts  of  endings  on  cells. 
Of  these  he  finds  that  in  the  unicellular  glands  of  the  frog's 
palate  one  frequently  finds  under  the  nucleus  a  small  blue  knob 
which  is  connected  with  a  fibre.  The  latter  cannot,  however,  be 
followed  farther. 

In  the  case  of  the  gland  cells  under  consideration,  there  can 
be  no  dmibt  that  the  nuclear  basket  is  connected  with  nerve 
fibres.  That  there  should  be  a  nerve  supply  to  the  gland  cells, 
seems  evident  from  the  experiments  of  Drasch  ('89),  Eberth 
('49)  and  Loeb  ('96)  on  Amphibian  glands,  and  we  have  in 
Plethodon  histological  evidence  of  such  supply.  The  well- 
known  influence  of  the  nervous  system  on  the  secretion  of  sweat, 
for  example,  may  be  also  mentioned  in  this  connection.  Herrick 
and  Coghill  ('98,  p.  51)  have  suggested  the  possibility  of  a  con- 
nection between  the  nerves  enveloping  the  glands,  and  the  gland 
cells,  but  were  not  able  to  demonstrate  it. 

The  objection  may  be  raised  that  we  are  dealing  here  with 
elastic  instead  of  nerve  fibres.  This  does  not  seem  possible  for 
several  reasons.  The  elastic  fibres,  as  has  been  said,  show  very 
little  variation  in  size,  and  never,  as  shown  by  staining  in  orcein, 
reach  the  excessive  fineness  of  the  nerve  fibres.  The  branching 
of  the  elastic  fibres  is  much  less  frequent  than  that  of  the  nerves, 
and,  in  clearest  distinction  the  former,  as  seen  upon  the  glands, 
take  an  almost  uniform  direction  even  in  branching,  straight 
toward  the  epidermis,  while  the  nerve  fibres  cross  and  recross  and 
branch  in  all  directions,  and  the  finest  twigs  show  varicosities 
which  are  never  seen  on  the  elastic  fibres.  The  general  effect  of 
the  brown  fibres  in  an  orcein  stain  is  entirely  different  from  that 
of  the  red  ones  in  Mallory's  stain,  and  leaves  no  doubt  of  the  dis- 
tinction here  set  forth  between  the  elastic  and  nervous  fibres. 


254  University  of  California  Publications.  [ZOOLOGY 

SUMMARY. 

1.  The    skin    glands    of   1'lrtliodon   oref/oiii-nxix,    as    of    most 
Amphibia,  are  of  two  kinds:  granular  and  mucous.     The  two  arc 
distinguished  by  the  character  and   staining  reaction   of  their 
secretions,  and  by  other  histological  features,  as  well  as  by  the 
sizes  of  the  glands. 

2.  The  bodies  of  the  large  glands  possess  an  investing  mus- 
culature, and  in  addition  the  ducts  have  both  dilator  and  con- 
strictor muscles  lying  in  the  epidermis. 

3.  The  granule  glauds  are  poison  in  character. 

4.  In  the  elaboration  and  ejaculation   of    the   secretion  the 
poison  glands  are  destroyed. 

5.  Renewal  takes  place  by  the  growth  into  all  the  old  glands 
of  a  new  and  smaller  gland,  which  is  mucous  in  character.     Tin- 
presence  of  this  smaller  sac  is  not  dependent  upon  the  removal 
of  the  secretion  of  the  large  glands,  for  whether  this  occurs  or 
not,  the  fundament  giving  the  mucous  reaction  is  found  in  all 
glands;  in  those  which  show  no  degeneration  as  well  as  in  those 
where  it  is  wide-spread. 

6.  The    growth    of   the    new  gland   is   dependent    upon    the 
removal  of  the  secretion  about  it.     There  is  evidence  that  even 
in  case  the  glands  are  hindered  in  their  development,  they  still 
secrete  mucus.     But  when  not  hemmed  in  by  the  heavy  granular 
contents  of  the  large  glands  they  grow  and  take  the  place  and 
very  probably  assume  the  function  of  the  old  glands  which  they 
replace. 

7.  Both  musculature  and  epithelium  of  the  granule  glands 
have  a  direct  nerve  supply.    The  gland  cells  are  surrounded  by  a 
basket  work  of  fibres,  which  in  some  eases  have  terminal  expan- 
sions lying  on  the  nuclei.     The  muscles  are  supplied  by  nerves 
with  typical  endings  of  expansions  or  bulbs,  as  well  as  by  fine 
twigs  without  terminal  expansions. 

Zoological  Laboratory, 

University  of  California, 
April  29,  1904. 


VOL.  i.]  l-'xii'flij. — Poison  Glands  of  Plethodon. 


BIBLIOGRAPHY. 


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Compt.  rend.  Ac.  Sei.,  Paris,  T.  108,  No.  13,  pp.  683-685. 

Eberth,  C.  J. 

1869.  Untersuchungen  zur  normalen  und  pathologischen  Anatomie  des 
Froschhaut.  Leipzig.  (Cited  by  Hoffmann,  Bronn's  Klass.  u. 
Ordn;  Seeck  '91.) 

Eberth,  C.  J.,  und  Bunge,  R. 

1892.  Die  Endigungen  der  Nerven  in  der  Haut  des  Frosches.  Anato- 
mische  Hefte,  Abth.  Arbeiten,  Hft.  5,  pp.  175-203.  PI.  XI,  14 
figures  in  text. 

Eckhard,  C. 

1849.  Ueber  den  Ban  der  Hautdriisen  der  Kroten  und  die  Abhilngigkeit, 
der  Kntleerung  ihres  Sekretes  vom  oentralen  Nervensystem. 
Arch.  f.  Anat.  u.  Physiol.,  1849,  pp.  425-428. 

Engelmann,  T.  W. 

1871.  Ueber  das  Vorkommen  und  Innervation  von  contractilen  Driisenzel- 

len  in  der  Froschhaut.     Pfliiger's  Archiv.,  Bd.  4,  pp.  1-3,   '72. 

1872.  Die  Hautdrusen  des  Frosches,  Ibid.,  Bd.  5,  pp.  498-538,  PI.  VII. 

Fraisse,  P. 

1885.  Die   Regeneration  von  Gesveben  und  Organen.     Kassel  u.  Berlin, 

1885,  164  pages,  3  plates.     (Cited  by  Vollmer,  1893,  p.  406.) 

Frenkel,  S. 

1886.  Nerv  und  Epithel   am  Froschlarvenschwanz.      Arch.  f.   Anat.   u. 

Physiol.  1886,  pp.  415-430.     PI.  XIII. 


VOL.  i.]  Esirrly.  —  /W.w/i  Qla/nds  of  Plethodon.  257 

Gratiolet,  P.— Cloez,  S. 

1851.  Notes  sur  les  propriete's  vSne'neuses  de  1'humeur  lactescente  que 

seVretent  les  pustules  pittances  de  la  Salamandre  terrestre  et  du 
Crapaud  commun.  Compt.  rend.  Ac.  Sci.  Paris,  T.  32,  pp. 
692-695. 

1852.  Nouvelles  observations    sur   le  venin    content!    dans   les    pustules 

cutanSes  des  Batracims.     Ibid,  T.  34,  pp.  729-732. 

Heidenhein,  M. 

1893d.  Die  Hautdriisen  der  Amphibien.  Sitzungsber.  d.  VViirzb.  physik. 
med.  Gesel.  No.  4,  p.  52.  (Cited  by  Vollmer,  '93,  p.  407.) 

18936.  Ueber  das  Vorkoramen  von  Intercellularbriicken  zwischen  glatten 
Muskelzellen  und  Epithelzellen  des  ailsseren  Keimblattes  und 
deren  theoretische  Bedeutung.  Anat.  Anz.  Jahrg.  8,  pp.  404- 
410.  1  figure  in  text. 

Hensche,  A. 

1856.     Ueber  die  Driisen  und  glatten  Muskeln  in  der  aiisserem  Haut  von 
Rana  temporaria.     Zeit.  f.  wiss.  Zool.,  Bd.  7,  pp.  273-282. 

Herrick,  C.  L.,  and  Coghill,  C.  E. 

1898.  The  Somatic  Equilibrium  and  the  Nerve-endings  in  the  Skin. 
Journ.  Comp.  Neurol.,  Vol.  8,  pp.  32-57.  Pis.  V-IX. 

Hoffmann,  C.  K. 

Amphibien.  Bronn's  Klassen  und  Ordnungen,  Bd.  6,  Abth.  2,  pp.  347- 
367. 

Hover,  H. 

1890.  Ueber  den  Nachweis  des  Mucins  in  Geweben  mittels  der  Farbe- 
method.  Arch.  f.  mikr.  Anat.,  Bd.  36,  pp.  310-374. 

Hubbard,  M.  E. 

1903.  Correlated  Protective  Devices  in  Some  California  Salamanders. 
Univ.  of  California  Pubs.,  Zoology,  Vol.  1,  No.  4,  pp.  157-168. 
PI.  XVI. 

Huber,  G.  C.,  and  Dewitt,  Mrs.  L.  M.  H. 

1898.  A  Contribution  to  the  Motor  Nerve-endings  and  on  the  Nerve-end- 
ings in  the  Muscle  Spindles.  Jour.  Comp.  Neurol.,  Vol.  7. 
pp.  169-230.  Pis.  XIV-XVIII. 

Junius,  P. 

1898.  Ueber  die  Hautdriisen  des  Frosches.  Arch.  f.  mikr.  Anat.,  Bd.  47, 
pp.  136-154.  PI.  X. 

Kallius,  E. 

1896.  Endigungen  sensibler  Nerven  bei  Wirbelthieren.  Ergebn.  d. 
Anat.  u.  Entwicklungsgesch.  (Merkel-Bonnet),  Bd.  5,  pp.  507- 
561. 


'J")S  University  of  California  Publications.  [ZOOI.OM 

Leydig,  F. 

1876a.     Ueber  die  allgemeine  Bedeekungen  der  Amphibieu.    Arch,  f.  mikr. 

Anat.  Bd.  12,  pp.  119-241. 
18766.     Die    Hautdecke    mid    HautsinBe8organe    der    1'rodelen.      Morph. 

•liihrb.,  Bd.  2,  pp.  287-318.     Pis.  XVIII-XXI. 

1892.  Zum  Integument  niederer  Wirbelthiere  abernmls.     Biolog.  Centbl., 

Bd.  12,  pp.  444-467. 
List,  J.  H. 

1889.     Ueber  den  feineren  Ban  Schleim  secernirender  Driisenzellen  nobst 

Bermerkungen  uber  dem  Secretionprocess.    Anat.  Anz.,   Jain';,'. 

4,  pp.  84-94. 
Loeb,  J. 

1896.     Sur  Theorie  des  Galvsnotropiwnng,     III.     Ueber  die  polare  Erre- 

gung  der   Hautdriisen  von  Amblystoma  durch   den    constanten 

Strom.       Pfliiger's    Ai-chiv.,   Bd.   65,    pp.   308-316.       12    (inures 

in  toxt. 

Macallum,  A.  B. 

1886.     Nerve-endings  in  the  Cutaneous  Epithelium  of  the  Tadpole.    Quart. 
Jour.  Micr.  Sci.,  Vol.  26,  pp.  53-70.     PI.  VI. 

Mallory,  F.  B. 

1900.     A  Contribution  to  Staining  Methods.     Jour.  Exper.  Med.,  Vol.  5, 
No.  1,  pp.  15-20. 

Massie,  J.  H. 

1894.     Glands  and  Nerve-endings   in  the    Skin   of   the   Tadpole.     Jour. 
Comp.  Neurol.,  Vol.  4,  pp.  7-12. 

Nicoglu,  P. 

1893.  Ueber  die   Hautdriisen  der  Amphibien.     Zeit.  f.  wiss.  Zool.,   Bd. 

56,  pp.  409-487.     Pis.  XXI-XXIII. 

Nussbaum,  M. 

1882.     Ueber  den  Thatigkeit  der  Driisen.     Arch.  f.  mikr.  Anat.,  Bd.  21,- 
pp.  296-351.     Pis.  XV-XVIII. 

Openchowski,  Th. 

1882.     Histologisches  zur  Innervation  der  Driisen.     Pfliiger's  Archiv.,  Bd. 

37,  pp.  223-233.     PI.  VI. 
Paulicki. 

1885.     Ueber  die  Haut  des  Axolotls.     Arch.  f.  mikr.  Anat.,  Bd.  24,  pp. 
120-171.     Pis.  VIII-IX. 

Pfitzner,  Wilh. 
1880.     Epidermis  des  Salamandres.     Morph.  Jahrb.,  Bd.  (i,   pp.  4()0-f>L>(i. 

Pis.  XXIV-XXV.     Also  Journ.  R.  Micr.  Soc.  (2),  Vol.,  pt.  1, 

pp.  218-224. 
1882.     Nervendigungen  ira  Epithel.     Morph.  Jahrb.,  Bd.  7,  pp.  726-745. 

1  plate. 


VOL.  i.]  Kxli'rly.  —  1'iiixoii  Gttmds  of  Plethodon.  _•">!> 


Phisalix,  C. 

1889.     Nouvellcs    experiences    sur    le    vcnin  de  hi  Siilamandre  terrestre. 
Coiupt.  rt-nil.  Ac.  Sci.  Paris,  T.  109,  pp.  4(15-407. 

Phisalix  and  Langlois. 

1889.     Action  physiologique  du  venin  de  la  Salamandre  terrestre.     Compt. 
rend.  Ac.  Sci.   I'aris,  T.  109,  pp.  482-48,'). 

Phisalix-Picot. 

1900.     Recherches  embryologiques,  histologiques  et  physiologiques  sur  les 
glandcs  a  vcnin  de  la  Salamandre  terrestre.     These  de  doctoral 
en  me'decine.     Paris,  1900. 
Roeber,  H. 

1869.     Ueber  das  elektromotorische  Verhalten  der  Froschhaut  bei  Reizung 
ihrer  Nerven.     Areh.  f.  Anat.  u.  Physiol.  1869,  pp.  633-649. 

Schuberg,  A. 
1903.     Untersuchungen  iiber  Zellverbindungen.     Zeit.  f.  wiss.  Zool.,  Bd. 

74,  Hf.  2,  pp.  156-325.     Pis.  IX-XV. 
Schultz,  P. 

1889.     Ueber  die  Giftdriisen  der  Kroten  und  Salamander.     Arch.  f.  mikr. 
Anat.,  Bd.  34,  pp.  11-57.     PI,  II. 

Schultze,  F.  E. 

1867.     Epithel—  und  Driisenzellen.     Arch.  f.  mikr.  Anat.,  Bd.  3,  pp.  137- 

202.     Pis.  VI-XII. 
Seeck,  O. 

1891.     Ueber  die  Hautdriisen  einiger  Amphibien.    Inaug.-Diss.  Dorpat. 

Stieda,  L. 

1865.  Ueber  den  Bau  der  Haut  des  Frosches.     Arch.  f.  Anat.  u.  Phys., 

1865,  pp.  52-67.     PI.  I. 

Szczesny,  O. 

1867.     Beitrage  zur  Kenntniss  der  Textur  der  Froschhaut.     Inaug.-Diss., 

Dorpat.     (Cited  by  Seeck,  '91.) 
Tonkoff,  W. 

1900.     Ueber  die  elastischen  Fasern  in  der  Froschhaut.     Arch.  f.  mikr. 

Anat.,  Bd.  57,  pp.  95-101.     PI.  VII. 
Vollmer,  E. 

1893.     Bin  Beitrag  zur  Lehre  von   den  Regeneration  speciel  der  Haut- 
driisen  der  Amphibien.     Areh.  f.  mikr.  Anat.,  Bd.  42,  pp.  405- 
423.     Pis.  XXIV-XXV. 
Weiss,  O. 

1899.     Ueber  die  Hautdrusen  von  Bufo  cinereus.      Arch.  £.  mikr.  Anat., 
Bd.  53,  pp.  385-396.     3  figures. 

Wiedersheim,  R. 

1886.     Lehrbuch  der  vergleichenden  Anatomie,  p.  25. 

Zalesky,  S. 

1866.  Ueber   das    Salamandarin.     Das   Gift    der    Salamandra    maculata. 

Med.  Chem.  Unters,  Bd.  J  1.  (Hoppe-Saeyler)  Berlin,  '66,  pp. 
85-116.     (Cited  by  Hoffmann  Klass.  u.  Ordn.) 


260  rith'frsity  of  California  Publications.  [ZOOLOGY 


LIST  OF  ABBREVIATIONS  USED   IN   THE   PLATES. 

con.m. — constrictor  muscle  fibres. 

c.t.b. — connective  tissue  bundles. 

c.t.l. — connective  tissue  layer  of  gland  walls. 

c.t. ---connective  tissue  in  epidermis. 

e.w. — cell  walls. 

d. — duct  of  gland. 

dil.m. — dilator  muscle  fibres. 

el.f. — elastic  fibres. 

ep. — epidermis. 

ep.m.c. — cell  containing  musculature  of  duct. 

fl.c. — funnel  cell. 

i.e.l. — inner  layer  of  corium. 

l.d.—  lumen  of  duct. 

l.gl. — lumen  of  gland. 

m.b. — muscle  bundles. 

m.e.l. — middle  layer  of  the  corium. 

m.f. — muscle  fibres. 

m.gl. — mucous  gland. 

m.n. — muscle  nucleus. 

n.c. — nerve  cord. 

n.e. — nerve  endings. 

n.fl.c. — nucleus  of  funnel  cell. 

n.f. — nerve  fibre. 

nuc.m.c. — nucleus  of  mucous  cell. 

nuc.p.c. — nucleus  of  poison  cell. 

nue.eji.m.c. — nucleus  of  muscle  cell  in  epidermis. 

o.c.l. — outer  layer  of  corium. 

p.fl.e. — processes  of  funnel  cells. 

p.gl. — poison  glands. 

pig.— pigment. 

prol.m.f. — prolongations  of  muscles  into  epidermis. 

rep.c. — replacement  cell  (and  nucleus). 

rep.gl. — replacement  glands. 

sec. — secretion. 

All  the  figures  were  drawn  with  the  Abb6  camera  lucida. 


ERRATA 

P.  251,  1.  31:   For  fuchsin-orange  G-anilin  blue, 
read  fuchsiu-orangeG-  anilin  blue. 

P.  259,  under  Zalesky  1866:  For  Bd.  J  1,  read  Bd.  1 ;  for  Saeyler,  read  Seyler. 
P.  264,  under  description  of  Fig.  16:  For  X  1650,  read  X  825. 
I'.  LliiG,  under  description  of  Fies.  21,  etc.:  For  X  1850    «•<•/•-•  ' 


PLATE  XX. 

Fig.  1. — Cross  section  of  entire  tail,  showing  position  on  dorsum  of  large 
poison  glands  (p. (/I.)  and  the  mucous  glands  (m.gl.)  chiefly  on  the 
ventral  side.  Diagrammatic  except  in  outlines  and  proportions 
of  parts.  Van  Gieson.X  22 

Fig.  2. — Mucus  gland  from  ventral  side  of  tail,  showing  large  lumen  (l.gl.), 
and  dark  staining,  angular  nuclei  (nuc.m.c.).  Lower  part  of 
funnel  cell  (fl.e.)  shown  in  epidermis  (ep)  which  is  not  repro- 
duced entire.  Benda's  iron  haematoxylin.  X  342 

Fig.  3. — Poison  gland  (p.gl.)  of  small  size  partly  replaced  by  ingrowing 
mucous  gland  (m.gl.).  Funnel  cell  (fl.c.)  shown  in  epidermis 
(ep.);  nuclei  (nuc.m.c.)  of  mucous  gland  darkly  stained  as  in 
Fig.  2.  Benda's  iron  haematoxylin.  X  342 

Fig.  4. — Outline  drawing  of  cross  section  of  duct  of  poison  gland  showing 
replacement  cells  of  the  funnel  (rep.c.)  rolled  one  within  the 
other,  the  funnel  cell  (fl.c.)  and  the  lumen  of  the  duct  (l.d.) 
Mallory's  conn,  tissue  stain.  X  875 

Fig.  5. — Portion  of  lower  part  of  poison  gland  showing  bundles  of  connec- 
tive tissue  (c.t.b.)  passing  from  the  inner  layer  of  the  corium 
(i.e./.)  to  the  connective  tissue  layer  of  the  wall  of  the  gland 
(e.t.l.)  Nuclei  (nue.p.c.)  and  walls  (e.tc.)  of  gland  cells.  Secre- 
tion not  shown  in  detail.  Mallory's  conn,  tissue  stain.  X  342 

Fig.  6. — One  side  of  median  longitudinal  section  of  duct  of  poison  gland 
showing  muscle  fibre  (»»./.)  and  its  nucleus  (m.n.)  and  the  pro- 
longation of  the  fibre  (prol.m.f.)  into  the  epidermis  (cp.). 
Compare  with  PI.  IV,  Fig.  27.  Mallory's  conn,  tissue  stain. 
X  280 

Fig.  7. — Branching  muscle  fibres  (m.f.)  from  lower  part  of  gland.  Mal- 
lory's conn.  tiss.  stain.  X  342 

Fig.  8. — Longitudinal  section  of  poison  gland  through  the  mouth  showing 
two  expansions  of  muscles  (m.f.}  in  which  the  nuclei  lie,  and 
portions  of  muscle  fibres.  Nucleus  of  funnel  cell  (n.JI.c.)  at 
duct  (d.).  Secretion  of  gland  not  shown.  Ferric-chloride 
haematoxylin.  X  342 


[262] 


BULL.  DEFT.  ZDDL.UNIY  CAL.VDL.I 


]  PLATE  XX 


.  >•-.:-•    .-.  ".u.  . 


PLATE  XXI. 

Fig.  9. — Elastic  fibres  (el.f.)  on  surface  of  gland.  Gland  wall  (c.t.l.)  in 
section  indicated;  also  nuclei  of  gland  cells.  The  elastic  fibres 
pass  through  the  inner  layer  of  the  corium  (i.c.L).  Tanxcr's 
oreein.  X  342 

Fig.  10. — Section  through  upper  pole  of  gland  at  one  side  of  the  duct,  show- 
ing cut  ends  of  muscle  fibres  (»«./.)  and  their  nuclei  (m.n.). 
From  cross  section  of  tail.  The  nuclei  in  this  figure  correspond 
in  position  to  that  shown  in  PI.  XX,  Fig.  6,  and  to  the  enlarge- 
ment of  the  fibres  shown  in  Fig.  8.  Mallory's  conn,  tissue  stain. 
X342 

Fig.  11. — Tangential  section  through  wall  of  gland  and  the  mouth,  from 
frontal  section  of  tail.  Muscle  fibres  (»(./.)  and  nuclei  (/«.«.) 
shown.  Funnel  cell(./Le.)  lining  duct  and  some  secretion  (sec.) 
in  lumen  of  duct  (l.d.).  Mallory's  conn,  tissue  stain.  X  342. 

Fig.  12. — Cross  section  of  gland  from  frontal  section  of  tail,  at  level  of 
muscle  nuclei  (m.n.).  Compare  with  Figs.  10  and  11.  Van 
Gieron's  stain.  X  400 

Fig.  13. — Cross  section  of  epidermis  at  upper  pole  of  poison  gland,  showing 
deep  lying  epidermal  cell  (ep.m.c.)  which  contains  the  con- 
strictor and  dilator  muscles  of  the  duct.  Mallory's  conn,  tissue 

X342 

Figs.  14  and  15. — Cross  sections  of  ducts  at  level  of  cell  described  in  Fig.  13, 
showing  constrictor  (con.m.)  and  dilator  muscles  (dil.m.).  In 
Fig.  14,  only  the  outer  ends  of  the  constrictor  fibre  appear.  In 
both  figures  are  shown  the  ends  of  the  muscle  fibres  (»«./.)  of 
the  glands,  in  the  epidermis,  and  the  connective  tissue  (c.t.) 
outside  the  nuscles.  The  nucleus  of  the  epidermal  muscle  cell 
is  shown  in  Fig.  14.  Mallory's  conn,  tissue  stain.  X  875 

Fig.  16. — Description  as  for  Figs.  14  and  15.  But  one  set  of  constrictor 
fibres  shown;  lumen  of  duct  (l.d.)  nearly  closed.  Mallory's 
conn,  tissue  stain.  X  1650 

Fig.  17. — Longitudinal  section  of  nearly  empty  poison  gland.  Secretion 
(sec.)  very  small  in  amount,  cell  walls  (c.w.)  distinct,  nuclei 
clear  and  of  irregular  shapes.  Semi-diagrammatic  in  unim- 
portant details.  Benda's  iron  haematoxylin.  X  34^ 


BULL. DEFT  ZQDL.UNIV  CAL.VDL!. 


[ESTEHLV]  PLATE  XXI. 


16 


C    D  E   DEL 


tis^T1 

Siv 


7/>> 


PLATE  XXII. 


Figs.  18,  19,  20. — Stages  in  replacement  of  small  poison  gland  (p.gl.)  by 
mucous  glands  (m.gl.)  from  sides  of  tail.  Mucous  nuclei  dark. 
Secretion  (sec.)  shown  in  poison  part  only.  Benda's  iron- 
haematoxylin.  >  342 

Figs.  21,  '22,  23,  24. —Tangential  sections  of  poison  glands,  showing  nerve 
endings  (ii.e.)  on  nuclei  of  poison  cells  (nuc.p.c.).  Mallory's 
conn,  tissue  stain.  Figs.  21,  22,  24.  X  1850.  Fig.  23.  X  875 

Figs.  25  and  26. — Tangential  section  of  wall  of  poison  glands,  showing  nerve 
endings  (n.e.)  on  muscles  (»»./.)•  Fig.  25,  Mallory's  conn, 
tissue  stain.  Fig.  26,  Cajal's  silver  nitrate-pyrogallic  acid. 

XH75 


[2661 


BULL.  DEFT  Z  DDL.  UN  iv  CAL.VDL!. 


[ESTERLY]  PLATE  XXII 


L'l 


23 


\  nuc.pr. 


PHOTO -LITH.HRITTaN  &RITi:a 


PLATE   XXIII. 

Fig.  '27. — Median  longitudinal  section  of  duet  of  poison  gland,  showing  pro- 
longation of  funnel  cell  (p.Jt.e.),  prolongation  of  muscles 
(l>rol.m.f.)  into  the  epidermis,  and  the  c-onnective  tissue  (c.t.) 
outside  them.  Replacement  cells  (rep.c.)  shown  with  processes 
extending  down  as  far  as  funnel  cell.  Mallory's  conn,  tissue 
stain.  X  1650 

Figs.  28,  29,  30. — Cross  sections  of  ducts,  showing  funnel  cells  (/.<•.),  gland 
muscles  (prnl.m.f.),  connective  tissue  (c.t.)  at  sides  of  duct  (</.), 
and  constrictor  and  dilator  muscles  (con. in,  dil.m.).  Mallory's 
conn,  tissue  stain.  *  1650 

Fig.  31. — Longitudinal  section  of  poison  gland,  showing  small  mucus  gland 
(m.gl.)  inside  it.  Large  gland  440  microns  by  180  microns; 
small  gland  90  microns  by  43  microns.  Mallory's  conn,  tissue 
stain.  X  1650 

Fig.  ',12. — Nerve-endings  (n.e.)  about  nucleus  of  poison  cell  (WHO.;;. c.).  Mal- 
lory's conn,  tissue  stain.  X  1650 


[268] 


BDLL.DEPT.ZDDL.UNIV  CAL.VDLI. 


, 


(tit  m.   S 


\ 


Tig.  28 


/„•,,/',„/: 

I'' 


• 


» — ^^ -* ~m    *  ••  »  •"»   " 


[ESTERLY]  PLATE  'XXIII. 


Fig- 


cttf.m. 


•—  con.ni 


Fig.  30 


PHOTC-l-ITH  BRITT 


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